Neurostimulation system for defining ideal multipole configurations at lead boundary

ABSTRACT

A system for an neurostimulator coupled to electrodes. The system comprises a input device configured for generating directional control signals, and memory storing ideal multipole configurations. The system further comprises control circuitry configured for defining the ideal multipole configurations relative to the electrodes in response to the directional control signals, determining a spatial relationship between at least one of the defined ideal multipole configurations and the maximum extent of the electrodes, modifying the defined ideal multipole configurations based on the determined spatial relationship, such that the modified ideal multipole configurations are spatially within the maximum extent of the electrodes, generating stimulation parameter sets respectively corresponding to the modified ideal multipole configurations, each stimulation parameter set defining relative amplitude values for the electrodes that emulate the respective modified ideal multipole configuration, and instructing the neurostimulator to convey electrical energy to the electrodes in accordance with the stimulation parameter sets.

RELATED APPLICATIONS

The present application is continuation of U.S. patent application Ser.No. 14/487,427, filed Sep. 16, 2014, now issued as U.S. Pat. No.9,387,328, which is continuation of U.S. patent application Ser. No.13/420,258, filed Mar. 14, 2012, now issued as U.S. Pat. No. 8,868,197,which claims the benefit under 35 U.S.C. § 119 to U.S. ProvisionalPatent Application Ser. No. 61/453,015, filed Mar. 15, 2011. Theforegoing application is hereby incorporated by reference into thepresent application in its entirety. The present utility application isfiled concurrently with U.S. patent application Ser. No. 13/420,060,entitled “NEUROSTIMULATION SYSTEM FOR DEFINING A GENERALIZED IDEALMULTIPOLE CONFIGURATION”, now issued as U.S. Pat. No. 8,909,350, U.S.patent application Ser. No. 13/420,040, entitled “NEUROSTIMULATIONSYSTEM AND METHOD FOR ROSTRO-CAUDALLY STEERING CURRENT USINGLONGITUDINAL IDEAL MULTIPOLE CONFIGURATIONS”, published as US2012/0170151, U.S. patent application Ser. No. 13/420,309, entitled“NEUROSTIMULATION SYSTEM AND METHOD FOR MEDIO-LATERALLY STEERING CURRENTUSING IDEAL MULTIPOLE CONFIGURATIONS”, now issued as U.S. Pat. No.8,595,871, and U.S. patent application Ser. No. 13/420,312, entitled“NEUROSTIMULATION SYSTEM FOR MATCHING IDEAL POLE SPACING WITH EFFECTIVEELECTRODE SEPARATION”, now issued as U.S. Pat. No. 9,014,820, thedisclosures of which are expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present inventions relate to tissue stimulation systems, and moreparticularly, to neurostimulation systems for programmingneurostimulation leads.

BACKGROUND OF THE INVENTION

Implantable neurostimulation systems have proven therapeutic in a widevariety of diseases and disorders. Pacemakers and Implantable CardiacDefibrillators (ICDs) have proven highly effective in the treatment of anumber of cardiac conditions (e.g., arrhythmias). Spinal CordStimulation (SCS) systems have long been accepted as a therapeuticmodality for the treatment of chronic pain syndromes, and theapplication of tissue stimulation has begun to expand to additionalapplications such as angina pectoralis and incontinence. Deep BrainStimulation (DBS) has also been applied therapeutically for well over adecade for the treatment of refractory chronic pain syndromes, and DBShas also recently been applied in additional areas such as movementdisorders and epilepsy. Further, in recent investigations, PeripheralNerve Stimulation (PNS) systems have demonstrated efficacy in thetreatment of chronic pain syndromes and incontinence, and a number ofadditional applications are currently under investigation. Furthermore,Functional Electrical Stimulation (FES) systems, such as the Freehandsystem by NeuroControl (Cleveland, Ohio), have been applied to restoresome functionality to paralyzed extremities in spinal cord injurypatients.

These implantable neurostimulation systems typically include one or moreelectrode carrying stimulation leads, which are implanted at the desiredstimulation site, and a neurostimulator (e.g., an implantable pulsegenerator (IPG)) implanted remotely from the stimulation site, butcoupled either directly to the neurostimulation lead(s) or indirectly tothe neurostimulation lead(s) via a lead extension. The neurostimulationsystem may further comprise an external control device to remotelyinstruct the neurostimulator to generate electrical stimulation pulsesin accordance with selected stimulation parameters.

Electrical stimulation energy may be delivered from the neurostimulatorto the electrodes in the form of an electrical pulsed waveform. Thus,stimulation energy may be controllably delivered to the electrodes tostimulate neural tissue. The combination of electrodes used to deliverelectrical pulses to the targeted tissue constitutes an electrodecombination, with the electrodes capable of being selectively programmedto act as anodes (positive), cathodes (negative), or left off (zero). Inother words, an electrode combination represents the polarity beingpositive, negative, or zero. Other parameters that may be controlled orvaried include the amplitude, width, and rate of the electrical pulsesprovided through the electrode array. Each electrode combination, alongwith the electrical pulse parameters, can be referred to as a“stimulation parameter set.”

With some neurostimulation systems, and in particular, those withindependently controlled current or voltage sources, the distribution ofthe current to the electrodes (including the case of theneurostimulator, which may act as an electrode) may be varied such thatthe current is supplied via numerous different electrode configurations.In different configurations, the electrodes may provide current orvoltage in different relative percentages of positive and negativecurrent or voltage to create different electrical current distributions(i.e., fractionalized electrode combinations).

As briefly discussed above, an external control device can be used toinstruct the neurostimulator to generate electrical stimulation pulsesin accordance with the selected stimulation parameters. Typically, thestimulation parameters programmed into the neurostimulator can beadjusted by manipulating controls on the external control device tomodify the electrical stimulation provided by the neurostimulator systemto the patient. Thus, in accordance with the stimulation parametersprogrammed by the external control device, electrical pulses can bedelivered from the neurostimulator to the stimulation electrode(s) tostimulate or activate a volume of tissue in accordance with a set ofstimulation parameters and provide the desired efficacious therapy tothe patient. The best stimulus parameter set will typically be one thatdelivers stimulation energy to the volume of tissue that must bestimulated in order to provide the therapeutic benefit (e.g., treatmentof pain), while minimizing the volume of non-target tissue that isstimulated.

However, the number of electrodes available, combined with the abilityto generate a variety of complex stimulation pulses, presents a hugeselection of stimulation parameter sets to the clinician or patient. Forexample, if the neurostimulation system to be programmed has an array ofsixteen electrodes, millions of stimulation parameter sets may beavailable for programming into the neurostimulation system. Today,neurostimulation system may have up to thirty-two electrodes, therebyexponentially increasing the number of stimulation parameters setsavailable for programming.

To facilitate such selection, the clinician generally programs theneurostimulator through a computerized programming system. Thisprogramming system can be a self-contained hardware/software system, orcan be defined predominantly by software running on a standard personalcomputer (PC). The PC or custom hardware may actively control thecharacteristics of the electrical stimulation generated by theneurostimulator to allow the optimum stimulation parameters to bedetermined based on patient feedback or other means and to subsequentlyprogram the neurostimulator with the optimum stimulation parameter setor sets, which will typically be those that stimulate all of the targettissue in order to provide the therapeutic benefit, yet minimizes thevolume of non-target tissue that is stimulated. The computerizedprogramming system may be operated by a clinician attending the patientin several scenarios.

For example, in order to achieve an effective result from SCS, the leador leads must be placed in a location, such that the electricalstimulation will cause paresthesia. The paresthesia induced by thestimulation and perceived by the patient should be located inapproximately the same place in the patient's body as the pain that isthe target of treatment. If a lead is not correctly positioned, it ispossible that the patient will receive little or no benefit from animplanted SCS system. Thus, correct lead placement can mean thedifference between effective and ineffective pain therapy. Whenelectrical leads are implanted within the patient, the computerizedprogramming system, in the context of an operating room (OR) mappingprocedure, may be used to instruct the neurostimulator to applyelectrical stimulation to test placement of the leads and/or electrodes,thereby assuring that the leads and/or electrodes are implanted ineffective locations within the patient.

Once the leads are correctly positioned, a fitting procedure, which maybe referred to as a navigation session, may be performed using thecomputerized programming system to program the external control device,and if applicable the neurostimulator, with a set of stimulationparameters that best addresses the painful site. Thus, the navigationsession may be used to pinpoint the volume of activation (VOA) or areascorrelating to the pain. Such programming ability is particularlyadvantageous for targeting the tissue during implantation, or afterimplantation should the leads gradually or unexpectedly move that wouldotherwise relocate the stimulation energy away from the target site. Byreprogramming the neurostimulator (typically by independently varyingthe stimulation energy on the electrodes), the volume of activation(VOA) can often be moved back to the effective pain site without havingto re-operate on the patient in order to reposition the lead and itselectrode array. When adjusting the volume of activation (VOA) relativeto the tissue, it is desirable to make small changes in the proportionsof current, so that changes in the spatial recruitment of nerve fiberswill be perceived by the patient as being smooth and continuous and tohave incremental targeting capability.

One known computerized programming system for SCS is called the BionicNavigator®, available from Boston Scientific NeuromodulationCorporation. The Bionic Navigator® is a software package that operateson a suitable PC and allows clinicians to program stimulation parametersinto an external handheld programmer (referred to as a remote control).Each set of stimulation parameters, including fractionalized currentdistribution to the electrodes (as percentage cathodic current,percentage anodic current, or off), may be stored in both the BionicNavigator® and the remote control and combined into a stimulationprogram that can then be used to stimulate multiple regions within thepatient.

Prior to creating the stimulation programs, the Bionic Navigator® may beoperated by a clinician in a “manual mode” to manually select thepercentage cathodic current and percentage anodic current flowingthrough the electrodes, or may be operated by the clinician in an“automated mode” to electrically “steer” the current along the implantedleads in real-time (e.g., using a joystick or joystick-like controls),thereby allowing the clinician to determine the most efficaciousstimulation parameter sets that can then be stored and eventuallycombined into stimulation programs. In the context of SCS, currentsteering is typically either performed in a rostro-caudal direction(i.e., along the axis of the spinal cord) or a medial-lateral direction(i.e., perpendicular to the axis of the spinal cord). The BionicNavigator® may use one of two ways to electrically steer the currentalong the implanted leads.

In one current steering method, known as “weaving,” the anode or anodesare moved around the cathode, while the cathode slowly progresses downthe sequence of electrodes. In the context of SCS, the active electrodecombinations typically used to implement the weaving sequence includes anarrow tripole (tightly spaced center cathode and two flanking anodes),narrow upper bipole (tightly spaced anode above cathode), wide upperbipole (widely spaced anode above cathode), wide tripole (widely spacedcenter cathode and two flanking anodes), wide lower bipole (widelyspaced anode below cathode), narrow lower bipole (narrowly spaced anodebelow cathode). In another current steering method, known as “panning,”a pre-defined electrode combination is shifted down the sequence ofelectrodes without changing the basic form of the electrode combination.These current steering methods may have different clinical uses (e.g.,finding the “sweet spot” in the case of panning, or shaping theelectrical field around the cathode in the case of weaving).

In the context of SCS, a volume of activation (VOA) will typically bedisplaced in concordance with the displacement of the cathode or groupof cathodes as electrical current is steering in a particular direction.In one method, the VOA may be rostro-caudally displaced along the spinalcord of the patient using, e.g., the weaving or panning steering currentsteering methods, in order to stimulate the rostro-caudal dermatomeassociated with the ailment to be treated. In another method known asTransverse Tripole Stimulation (TTS), wherein a tripole electrodeconfiguration consisting of a central cathode and two flanking anodes isused, to selectively stimulate dorsal column (DC) nerve fibers withoutstimulating the dorsal root (DR) nerve fibers typically associated withpainful or otherwise uncomfortable side-effects. To target a populationof DC nerve fibers where medio-lateral fiber distribution is mapped intorostro-caudal dermatomes, steering of current onto the DC nerve fibersis a critical component of TTS. Typically, in the three-column electrodearrangement, steering of current in TTS can be achieved by adjusting theintensity of the flanking anodes, as described in U.S. patentapplication Ser. No. 12/508,407, entitled “System and Method forIncreasing Relative Intensity Between Cathodes and Anodes ofNeurostimulation System,” which is expressly incorporated herein byreference.

The Bionic Navigator® presently performs current steering in accordancewith a steering or navigation table. For example, an exemplarynavigation table, which includes a series of reference electrodecombinations (e.g., for a lead of 8 electrodes) with associatedfractionalized current values (i.e., fractionalized electrodeconfigurations), can be used to gradually steer electrical current fromone basic electrode combination to the next, thereby electronicallysteering the volume of activation (VOA) along the leads.

While the use of navigation tables have proven to be useful in steeringelectrical current between electrodes in an efficient manner, that arecertain inherent disadvantages associated with navigation tables. Forexample, assuming a current step size of 5% in the navigation table,there are literally billions of fractionalized electrode configurationsthat can be selected. However, due to memory and time constraints, onlya limited number of fractionalized electrode configurations are storedwithin the navigation table. Therefore, not every desired electrodecombination and associated fractionalized current values can berepresented within a steering table.

Furthermore, a substantial amount of time and effort must be spent indeveloping navigation tables for each new lead design, therebypresenting a bottleneck for lead development. For example, each steeringtable must take into account the variability in electrode position orstimulation input. The variability in electrode position may be due to,e.g., a different lead model, different lead configurations (e.g., aclosely spaced side-by-side configuration, a closely spaced top-bottomconfiguration, a widely spaced top-bottom configuration, or a widelyspaced side-by-side configuration), stagger of the leads, etc. Thevariability in stimulation input may be due to, e.g., the development orinclusion of additional steerable fields (e.g., medio-lateral tripolesteering), upgrades in steering controls (e.g., focusing/blurring offields, anode intensification or de-intensification (i.e., increasing ordecreasing local anodic current relative to cathodic current), currentsteering from different screens, etc. Because the implementation of newnavigation tables must take into account all leads that are to be usedwith the IPG, as well as the different lead positions, this challengeslows the ability to include new navigation features in the system.

Furthermore, if the remote control needs to be reprogrammed; forexample, if the patient returns to a physician's office to be refittedto improve the stimulation therapy provided by the neurostimulator, theclinician may have to start the fitting from scratch. In particular,while the remote control is capable of uploading the stimulationparameter sets to the Bionic Navigator® to aid in reprogramming theremote control, they may be different from any stimulation parametersets that are capable of being generated using the navigation table dueto the limited number of fractionalized electrode configurations withinthe navigation table; that is, the fractionalized electrodeconfigurations currently stored in the remote control may not match anyfractionalized electrode configurations stored in the navigation tablebecause they were originally generated when the Bionic Navigator® wasoperated in the manual mode.

In any event, if the stimulation parameter sets uploaded from the remotecontrol to the Bionic Navigator® do not identically match anystimulation parameter set corresponding to a fractionalized electrodeconfiguration stored in the navigation table, it cannot be used as astarting point in reprogramming the remote control/IPG. As a result, theamount of time required to reprogram the remote control/IPG may be aslong as the amount of time required to originally program the remotecontrol/IPG with the Bionic Navigator®. Because programming the remotecontrol can be quite complex, even when the Bionic Navigator® isoperated in the navigation mode, the time lost as a result of having toreprogram the remote control/IPG from scratch, can be quite significant.

In one novel method, described in U.S. Pat. No. 8,412,345, which isincorporated herein by reference, a stimulation target in the form of anideal target pole (e.g., an ideal bipole or tripole) is defined and thestimulation parameters, including the fractionalized current values oneach of the electrodes, are computationally determined in a manner thatemulates these ideal target poles. It can be appreciated that currentsteering can be implemented by moving the ideal target poles about theleads, such that the appropriate fractionalized current values for theelectrodes are computed for each of the various positions of the idealtarget pole. As a result, the current steering can be implemented usingan arbitrary number and arrangement of electrodes, thereby solving theafore-described problems.

While the computation of stimulation parameters to emulate ideal targetpoles is quite useful, there remains a need to provide a moregeneralized format for ideal target poles to provide more flexibility tosteering current in an arbitrary direction. For example, ideal targetpoles aligned along the longitudinal axis of the spinal cord of apatient may be optimum when steering current in a rostro-caudal(longitudinal) direction, but may not be optimum when steering currentin a medial-lateral (transverse) direction. Likewise, ideal target polesaligned perpendicular to the longitudinal axis of the spinal cord of apatient may be optimum when steering current in a medial-lateral(transverse) direction, but may not be optimum when steering current ina rostro-caudal direction (longitudinal). There also remains a need forimproved techniques using ideal target poles to steer current in therostro-caudal direction and the medial-lateral direction.

Furthermore, because there a limited number of electrodes when steeringcurrent in a particular direction using arbitrarily defined targetpoles, there remains a need to modify the current steering on-the-fly toprevent any target poles from being moved outside the maximum extent ofthe electrode array. Also, for ideal multipole configurations, whichinclude at least one ideal cathode and at least one ideal anode, it isdesirable to match the spacing between the ideal cathode(s) and idealanode(s) with the spacing of the physical electrodes in order tominimize dilution of the electrical current on multiple electrodes,which may otherwise cause amplitude fluctuation or a non-focusedstimulation region during current steering. However, because differenttypes of neurostimulation leads have different electrode separations, acurrent steering algorithm that is designed for a particular electrodeseparation cannot be used for other electrode separations. Furthermore,when multiple neurostimulation leads are used, the spacings between theelectrodes will typically not be uniform, thereby providing a challengewhen attempting to match the ideal cathode/anode spacings with thespacings of the physical electrodes.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present inventions, a system for anelectrical neurostimulator coupled to a plurality of electrodes having amaximum extent is provided. As one example, if the electrode array is alinear electrode array, the maximum extent may be coincident with anelectrode at the end of the linear electrode array.

The system comprises a user-controlled input device configured forgenerating directional control signals. In one embodiment, theuser-control input device includes a control element, a continualactuation of which generates the control signals. The user-controlledinput device may comprise, e.g., one or more of a graphical arrow, ajoystick, a touchpad, a button pad, a group of keyboard arrow keys, amouse, a roller ball tracking device, and horizontal and verticalrocker-type arm switches for generating the directional control signals.The system further comprises memory storing a plurality of idealmultipole configurations (e.g., at least one ideal bipole configurationand at least one ideal tripole configuration).

The system further comprises control circuitry configured for definingthe plurality of ideal multipole configurations relative to theelectrode array in response to the directional control signals,determining a spatial relationship between at least one of the definedplurality of ideal multipole configurations and the maximum extent ofthe electrode array, and modifying the defined plurality of the idealmultipole configurations based on the determined spatial relationship,such that the modified plurality of the ideal multipole configurationsis spatially within the maximum extent of the electrode array.

The control circuitry may modify the defined plurality of idealmultipole configuration in a variety of manners; e.g., by eliminatingone or more of the defined multipole configuration(s), modifying when apole of the same polarity is initially displaced during the definedideal multipole configurations(s), displacing a pole for one or more ofthe defined ideal multipole configuration(s), displacing poles ofdifferent polarities relative to each other for one or more of thedefined ideal multipole configuration(s), etc.

If the poles of different polarities are to be displaced relative toeach other, the memory, for each of the defined ideal multipoleconfiguration(s), may store a variable value defining a spatialrelationship between the poles of the different polarities (e.g. anabsolute distance between the poles of different polarities), in whichcase, the control circuitry may be configured for displacing the polesof different polarities relative to each other for ideal multipoleconfiguration(s) by modifying the respective at least one variable value(e.g., by decreasing the variable value(s)). The defined plurality ofideal multipole configurations may include a defined plurality of wideideal bipole/tripole configurations and a defined plurality of narrowideal bipole/tripole configurations. In this case, the ideal multipoleconfiguration(s) with which the variable values are associated mayinclude the defined plurality of wide ideal bipole/tripoleconfigurations, and the control circuitry may be configured fordisplacing the poles of different polarities relative to each other forthe these multipole configuration(s) by decreasing the respectivevariable value(s).

In one embodiment, the defined plurality of narrow ideal bipole/tripoleconfigurations initially comprises a narrow upper ideal bipoleconfiguration and a narrow lower ideal bipole configuration, and thedefined plurality of wide ideal bipole/tripole configurations initiallycomprises two identical wide upper ideal bipole configurations, a firstwide ideal tripole configuration, and two identical wide lower idealbipole configurations. In this case, the control circuitry may beconfigured for decreasing the variable values associated with a firstone of the two identical wide upper ideal bipole configurations and afirst one of the two identical wide lower ideal bipole configurations toa first identical value, changing one of a second one of the twoidentical wide upper ideal bipole configurations and a second one of thetwo identical wide lower ideal bipole configurations to a second wideideal tripole configuration, modifying a relative intensity between thepoles of different polarities of the second wide ideal tripoleconfiguration, decreasing the variable value associated with the secondwide ideal tripole configuration (e.g., to the first identical value),and modifying a relative intensity between the poles of differentpolarities of the first wide ideal tripole configuration.

The control circuitry is further configured generating a plurality ofstimulation parameter sets respectively corresponding to the modifiedideal multipole configurations, with each stimulation parameter setdefining relative amplitude values for the plurality of electrodes thatemulate the respective ideal multipole configuration, and instructingthe electrical neurostimulator to convey electrical energy to theplurality of electrodes in accordance with the plurality of stimulationparameter sets. In an optional embodiment, the system further comprisestelemetry circuitry, wherein the control circuitry is configured fortransmitting the stimulation parameter sets to the neurostimulationdevice via the telemetry circuitry. In another optional embodiment, thesystem further comprises a housing containing the user input device, thememory, and the control circuitry.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of a Spinal cord Stimulation (SCS) systemconstructed in accordance with one embodiment of the present inventions;

FIG. 2 is a perspective view of the arrangement of the SCS system ofFIG. 1 with respect to a patient;

FIG. 3 is a profile view of an implantable pulse generator (IPG) and asurgical paddle lead used in the SCS system of FIG. 1;

FIG. 4 is a profile view of an implantable pulse generator (IPG) andpercutaneous leads used in the SCS system of FIG. 1;

FIG. 5 is front view of a remote control (RC) used in the SCS system ofFIG. 1;

FIG. 6 is a block diagram of the internal components of the RC of FIG.4;

FIG. 7 is a block diagram of the internal components of a clinician'sprogrammer (CP) used in the SCS system of FIG. 1;

FIG. 8 is a plan view of a user interface of the CP of FIG. 7 forprogramming the IPG of FIG. 3;

FIG. 9 is a plan view of generalized ideal multipole that can be used bythe CP of FIG. 7 to define different ideal multipole configurations;

FIG. 10 is a plan view of a longitudinal ideal tripole configurationthat can be derived from the generalized ideal multipole of FIG. 9;

FIG. 11 is a plan view of a transverse ideal tripole configuration thatcan be derived from the generalized ideal multipole of FIG. 9;

FIG. 12 is a plan view of a rotated ideal tripole configuration that canbe derived from the generalized ideal multipole of FIG. 9;

FIG. 13 is a plan view of an asymmetric ideal tripole configuration thatcan be derived from the generalized ideal multipole of FIG. 9;

FIG. 14 is a plan view of a generalized ideal longitudinal tripole thatcan be used by the CP of FIG. 7 to define different ideal bipole/tripoleconfigurations;

FIG. 15 is a sequence of different ideal bipole/tripole configurationsthat can be derived from the ideal longitudinal tripole of FIG. 14 torostro-caudally displace a volume of activation;

FIG. 16 is a plot illustrating a weaving space for the sequence ofbipole/tripole configurations illustrated in FIG. 15;

FIG. 17 is a plot illustrating the weaving space of FIG. 16,particularly showing the fine resolution incremental steps between theideal bipole/tripole configurations;

FIG. 18 is a plot illustrating the weaving space of FIG. 16,particularly showing the coarse resolution incremental steps between theideal bipole/tripole configurations;

FIG. 19 is another sequence of different ideal bipole/tripoleconfigurations that can be derived from the ideal longitudinal tripoleof FIG. 14 to rostro-caudally displace a volume of activation;

FIG. 20 is a plot illustrating a weaving space for the sequence of idealbipole/tripole configurations illustrated in FIG. 19;

FIG. 21 is a plan view of a generalized ideal multipole that can be usedby the CP of FIG. 7 to define different ideal multipole configurations;

FIG. 22a is a sequence of electrode configurations that can be definedby the CP of FIG. 7 to medio-laterally displace a volume of activation;

FIG. 22b is a sequence of ideal multipole configurations that can bederived from the generalized ideal multipole of FIG. 21 tomedio-laterally displace a volume of activation;

FIG. 22c is plot of the different parameter values used to transitionbetween the ideal multipole configurations of FIG. 22 b;

FIG. 23 is still another sequence of different ideal bipole/tripoleconfigurations that can be derived from the ideal longitudinal tripoleof FIG. 14 to rostro-caudally displace a volume of activation, whereinone of the ideal bipole/tripole configurations exceeds the maximumextent of the electrode array;

FIG. 24 is a corrected sequence of the ideal bipole/tripoleconfigurations shown in FIG. 23, wherein none of the idealbipole/tripole configurations exceeds the maximum extent of theelectrode array;

FIG. 25 is a plot illustrating a weaving space for the sequence of idealbipole/tripole configurations illustrated in FIG. 24;

FIG. 26 is a plot illustrating a weaving space for a sequence of idealbipole/tripole configurations that may be varied to prevent an idealbipole/tripole configuration from exceeding the maximum extent of theelectrode array;

FIGS. 27a-27c are plots of a weaving space illustrating the manner inwhich the ideal bipole/tripole configurations are varied to prevent anideal bipole/tripole configuration from exceeding a maximum rostralextent of the electrode array;

FIGS. 28a-28c are plots of a weaving space illustrating the manner inwhich the ideal bipole/tripole configurations are varied to prevent anideal bipole/tripole configuration from exceeding a maximum caudalextent of the electrode array;

FIG. 29 is a corrected sequence of the ideal bipole/tripoleconfigurations shown in FIG. 23, wherein the ideal tripoleconfigurations and the ideal upper ideal bipole configurations areeliminated to prevent the ideal bipole/tripole configurations fromexceeding the maximum rostral extent of the electrode array;

FIG. 30 is a plot illustrating a weaving space for the sequence of lowerideal bipole configurations illustrated in FIG. 29;

FIG. 31a is a plan view of three percutaneous neurostimulation leads andan ideal tripole configuration aligned with the center neurostimulationlead, wherein the separation between the poles of the ideal tripoleconfiguration is the same as the electrode spacing of the centerneurostimulation lead;

FIG. 31b is a plan view of three staggered percutaneous neurostimulationleads and an ideal tripole configuration rotated relative to the centerneurostimulation lead, wherein the separation between the poles of theideal tripole configuration is not the same as the electrode spacing ofthe center neurostimulation lead;

FIG. 32a is a plan view of two staggered percutaneous neurostimulationleads with a point in space at which an effective electrode separationcan be estimated in the rostral direction or the caudal direction;

FIG. 32b is a plan view of two widely spaced staggered percutaneousneurostimulation leads, wherein electrodes on the right neurostimulationlead is not taken into account when estimating an effective electrodeseparation at a reference electrode on the left neurostimulation lead;

FIG. 32c is a plan view of two narrowly spaced staggered percutaneousneurostimulation leads, wherein an electrode on the rightneurostimulation lead dominates the estimation of an effective electrodeseparation at a reference electrode on the left neurostimulation lead;and

FIG. 33 is a flow diagram illustrating one method performed in the CP ofFIG. 8 to estimate an effective electrode separation at a point inspace, which can be utilized to define a spacing between one polelocated at the point in space and another pole of an ideal multipoleconfiguration.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The description that follows relates to a spinal cord stimulation (SCS)system. However, it is to be understood that while the invention lendsitself well to applications in SCS, the invention, in its broadestaspects, may not be so limited. Rather, the invention may be used withany type of implantable electrical circuitry used to stimulate tissue.For example, the present invention may be used as part of a pacemaker, adefibrillator, a cochlear stimulator, a retinal stimulator, a stimulatorconfigured to produce coordinated limb movement, a cortical stimulator,a deep brain stimulator, peripheral nerve stimulator, microstimulator,or in any other neurostimulator configured to treat urinaryincontinence, sleep apnea, shoulder sublaxation, headache, etc.

Turning first to FIG. 1, an exemplary SCS system 10 generally comprisesat least one implantable neurostimulation lead 12, an implantable pulsegenerator (IPG) 14 (or alternatively RF receiver-stimulator), anexternal remote control RC 16, a Clinician's Programmer (CP) 18, anExternal Trial Stimulator (ETS) 20, and an external charger 22.

The IPG 14 is physically connected via one or more lead extensions 24 tothe neurostimulation lead 12, which carries a plurality of electrodes 26arranged in an array. The neurostimulation lead 12 is illustrated as asurgical paddle lead in FIG. 1, although as will be described in furtherdetail below, one or more percutaneous stimulation leads can be used inplace of the surgical paddle lead 12. As will also be described infurther detail below, the IPG 14 includes pulse generation circuitrythat delivers electrical stimulation energy in the form of a pulsedelectrical waveform (i.e., a temporal series of electrical pulses) tothe electrode array 26 in accordance with a set of stimulationparameters.

The ETS 20, which has similar pulse generation circuitry as the IPG 14,also provides electrical stimulation energy to the electrode array 26 inaccordance with a set of stimulation parameters. The major differencebetween the ETS 20 and the IPG 14 is that the ETS 20 is anon-implantable device that is used on a trial basis after theneurostimulation leads 12 have been implanted and prior to implantationof the IPG 14, to test the responsiveness of the stimulation that is tobe provided. Thus, any functions described herein with respect to theIPG 14 can likewise be performed with respect to the ETS 20. Furtherdetails of an exemplary ETS are described in U.S. Pat. No. 6,895,280,which is expressly incorporated herein by reference.

The RC 16 may be used to telemetrically control the ETS 20 via abi-directional RF communications link 32. Once the IPG 14 andstimulation lead 12 are implanted, the RC 16 may be used totelemetrically control the IPG 14 via a bi-directional RF communicationslink 34. Such control allows the IPG 14 to be turned on or off and to beprogrammed with different stimulation programs after implantation. Oncethe IPG 14 has been programmed, and its power source has been charged orotherwise replenished, the IPG 14 may function as programmed without theRC 16 being present.

The CP 18 provides clinician detailed stimulation parameters forprogramming the IPG 14 and ETS 20 in the operating room and in follow-upsessions. The CP 18 may perform this function by indirectlycommunicating with the IPG 14 or ETS 20, through the RC 16, via an IRcommunications link 36. Alternatively, the CP 18 may directlycommunicate with the IPG 14 or ETS 20 via an RF communications link (notshown).

The external charger 22 is a portable device used to transcutaneouslycharge the IPG 14 via an inductive link 38. For purposes of brevity, thedetails of the external charger 22 will not be described herein. Detailsof exemplary embodiments of external chargers are disclosed in U.S. Pat.No. 6,895,280, which has been previously incorporated herein byreference. Once the IPG 14 has been programmed, and its power source hasbeen charged by the external charger 22 or otherwise replenished, theIPG 14 may function as programmed without the RC 16 or CP 18 beingpresent.

As shown in FIG. 2, the electrode lead 12 is implanted within the spinalcolumn 42 of a patient 40. The preferred placement of the electrode lead12 is adjacent, i.e., resting upon, the spinal cord area to bestimulated. Due to the lack of space near the location where theelectrode leads 12 exit the spinal column 42, the IPG 14 is generallyimplanted in a surgically-made pocket either in the abdomen or above thebuttocks. The IPG 14 may, of course, also be implanted in otherlocations of the patient's body. The lead extension 24 facilitateslocating the IPG 14 away from the exit point of the electrode leads 12.As there shown, the CP 18 communicates with the IPG 14 via the RC 16.

Referring to FIG. 3, the IPG 14 comprises an outer case 44 for housingthe electronic and other components (described in further detail below),and a connector 46 to which the proximal end of the neurostimulationlead 12 mates in a manner that electrically couples the electrodes 26 tothe internal electronics (described in further detail below) within theouter case 44. The outer case 44 is composed of an electricallyconductive, biocompatible material, such as titanium, and forms ahermetically sealed compartment wherein the internal electronics areprotected from the body tissue and fluids. In some cases, the outer case44 may serve as an electrode.

In the embodiment illustrated in FIG. 3, the neurostimulation lead 12takes the form of a surgical paddle lead 12 on which the electrodes 26(in this case, electrodes E1-E22) are carried. The electrodes 26 arearranged in a two-dimensional array in four columns along the axis ofthe neurostimulation lead 12. In the illustrated embodiment, theelectrodes 26 are arranged in two inner columns of electrodes 26′(electrodes E7-E16), and two outer columns of electrodes 26″ (electrodesE1-E6 and E17-E22) that flank and are longitudinally offset from theinner electrode columns. In other embodiments, the outer and innerelectrode columns may not be longitudinally offset from each other. Theactual number of leads and electrodes will, of course, vary according tothe intended application. Further details regarding the construction andmethod of manufacture of surgical paddle leads are disclosed in U.S.patent application Ser. No. 11/319,291, entitled “Stimulator Leads andMethods for Lead Fabrication,” and U.S. Pat. No. 7,987,000, thedisclosures of which are expressly incorporated herein by reference.

In an alternative embodiment illustrated in FIG. 4, the neurostimulationlead 12 takes the form of a percutaneous stimulation lead on which theelectrodes 12 (in this case, electrodes E1-E8) are disposed as ringelectrodes. Although only one percutaneous stimulation lead 12 is shown,multiple percutaneous stimulation leads (e.g., two), can be used withthe SCS system 10. The actual number and shape of leads and electrodeswill, of course, vary according to the intended application. Furtherdetails describing the construction and method of manufacturingpercutaneous stimulation leads are disclosed in U.S. Pat. Nos.8,019,439, and 7,650,184, the disclosures of which are expresslyincorporated herein by reference.

As will be described in further detail below, the IPG 14 includes pulsegeneration circuitry that provides electrical conditioning andstimulation energy in the form of a pulsed electrical waveform to theelectrode array 26 in accordance with a set of stimulation parametersprogrammed into the IPG 14. Such stimulation parameters may compriseelectrode combinations, which define the electrodes that are activatedas anodes (positive), cathodes (negative), and turned off (zero),percentage of stimulation energy assigned to each electrode(fractionalized electrode configurations), and electrical pulseparameters, which define the pulse amplitude (measured in milliamps orvolts depending on whether the IPG 14 supplies constant current orconstant voltage to the electrode array 26), pulse width (measured inmicroseconds), pulse rate (measured in pulses per second), and burstrate (measured as the stimulation on duration X and stimulation offduration Y).

Electrical stimulation will occur between two (or more) activatedelectrodes, one of which may be the IPG case. Simulation energy may betransmitted to the tissue in a monopolar or multipolar (e.g., bipolar,tripolar, etc.) fashion. Monopolar stimulation occurs when a selectedone of the lead electrodes 26 is activated along with the case of theIPG 14, so that stimulation energy is transmitted between the selectedelectrode 26 and case. Bipolar stimulation occurs when two of the leadelectrodes 26 are activated as anode and cathode, so that stimulationenergy is transmitted between the selected electrodes 26. For example,an electrode on one lead 12 may be activated as an anode at the sametime that an electrode on the same lead or another lead 12 is activatedas a cathode. Tripolar stimulation occurs when three of the leadelectrodes 26 are activated, two as anodes and the remaining one as acathode, or two as cathodes and the remaining one as an anode. Forexample, two electrodes on one lead 12 may be activated as anodes at thesame time that an electrode on another lead 12 is activated as acathode.

The stimulation energy may be delivered between electrodes as monophasicelectrical energy or multiphasic electrical energy. Monophasicelectrical energy includes a series of pulses that are either allpositive (anodic) or all negative (cathodic). Multiphasic electricalenergy includes a series of pulses that alternate between positive andnegative. For example, multiphasic electrical energy may include aseries of biphasic pulses, with each biphasic pulse including a cathodic(negative) stimulation phase and an anodic (positive) recharge phasethat is generated after the stimulation phase to prevent direct currentcharge transfer through the tissue, thereby avoiding electrodedegradation and cell trauma. That is, charge is delivered through theelectrode-tissue interface via current at an electrode during astimulation period (the length of the stimulation pulse), and thenpulled back off the electrode-tissue interface via an oppositelypolarized current at the same electrode during a recharge period (thelength of the recharge pulse).

In the illustrated embodiment, IPG 14 can individually control themagnitude of electrical current flowing through each of the electrodes.In this case, it is preferred to have a current generator, whereinindividual current-regulated amplitudes from independent current sourcesfor each electrode may be selectively generated. Although this system isoptimal to take advantage of the invention, other stimulators that maybe used with the invention include stimulators having voltage regulatedoutputs. While individually programmable electrode amplitudes areoptimal to achieve fine control, a single output source switched acrosselectrodes may also be used, although with less fine control inprogramming. Mixed current and voltage regulated devices may also beused with the invention. Further details discussing the detailedstructure and function of IPGs are described more fully in U.S. Pat.Nos. 6,516,227 and 6,993,384, which are expressly incorporated herein byreference.

It should be noted that rather than an IPG, the SCS system 10 mayalternatively utilize an implantable receiver-stimulator (not shown)connected to the neurostimulation leads 12. In this case, the powersource, e.g., a battery, for powering the implanted receiver, as well ascontrol circuitry to command the receiver-stimulator, will be containedin an external controller inductively coupled to the receiver-stimulatorvia an electromagnetic link. Data/power signals are transcutaneouslycoupled from a cable-connected transmission coil placed over theimplanted receiver-stimulator. The implanted receiver-stimulatorreceives the signal and generates the stimulation in accordance with thecontrol signals.

Referring now to FIG. 5, one exemplary embodiment of an RC 16 will nowbe described. As previously discussed, the RC 16 is capable ofcommunicating with the IPG 14, CP 18, or ETS 20. The RC 16 comprises acasing 50, which houses internal componentry (including a printedcircuit board (PCB)), and a lighted display screen 52 and button pad 54carried by the exterior of the casing 50. In the illustrated embodiment,the display screen 52 is a lighted flat panel display screen, and thebutton pad 54 comprises a membrane switch with metal domes positionedover a flex circuit, and a keypad connector connected directly to a PCB.In an optional embodiment, the display screen 52 has touch screencapabilities. The button pad 54 includes a multitude of buttons 56, 58,60, and 62, which allow the IPG 14 to be turned ON and OFF, provide forthe adjustment or setting of stimulation parameters within the IPG 14,and provide for selection between screens.

In the illustrated embodiment, the button 56 serves as an ON/OFF buttonthat can be actuated to turn the IPG 14 ON and OFF. The button 58 servesas a select button that allows the RC 16 to switch between screendisplays and/or parameters. The buttons 60 and 62 serve as up/downbuttons that can be actuated to increment or decrement any ofstimulation parameters of the pulse generated by the IPG 14, includingpulse amplitude, pulse width, and pulse rate. For example, the selectionbutton 58 can be actuated to place the RC 16 in a “Pulse AmplitudeAdjustment Mode,” during which the pulse amplitude can be adjusted viathe up/down buttons 60, 62, a “Pulse Width Adjustment Mode,” duringwhich the pulse width can be adjusted via the up/down buttons 60, 62,and a “Pulse Rate Adjustment Mode,” during which the pulse rate can beadjusted via the up/down buttons 60, 62. Alternatively, dedicatedup/down buttons can be provided for each stimulation parameter. Ratherthan using up/down buttons, any other type of actuator, such as a dial,slider bar, or keypad, can be used to increment or decrement thestimulation parameters. Further details of the functionality andinternal componentry of the RC 16 are disclosed in U.S. Pat. No.6,895,280, which has previously been incorporated herein by reference.

Referring to FIG. 6, the internal components of an exemplary RC 16 willnow be described. The RC 16 generally includes a processor 64 (e.g., amicrocontroller), memory 66 that stores an operating program forexecution by the processor 64, as well as stimulation parameter sets ina navigation table (described below), input/output circuitry, and inparticular, telemetry circuitry 68 for outputting stimulation parametersto the IPG 14 and receiving status information from the IPG 14, andinput/output circuitry 70 for receiving stimulation control signals fromthe button pad 54 and transmitting status information to the displayscreen 52 (shown in FIG. 5). As well as controlling other functions ofthe RC 16, which will not be described herein for purposes of brevity,the processor 64 generates new stimulation parameter sets in response tothe user operation of the button pad 54. These new stimulation parametersets would then be transmitted to the IPG 14 via the telemetry circuitry68. Further details of the functionality and internal componentry of theRC 16 are disclosed in U.S. Pat. No. 6,895,280, which has previouslybeen incorporated herein by reference.

As briefly discussed above, the CP 18 greatly simplifies the programmingof multiple electrode combinations, allowing the user (e.g., thephysician or clinician) to readily determine the desired stimulationparameters to be programmed into the IPG 14, as well as the RC 16. Thus,modification of the stimulation parameters in the programmable memory ofthe IPG 14 after implantation is performed by a user using the CP 18,which can directly communicate with the IPG 14 or indirectly communicatewith the IPG 14 via the RC 16. That is, the CP 18 can be used by theuser to modify operating parameters of the electrode array 26 near thespinal cord.

As shown in FIG. 2, the overall appearance of the CP 18 is that of alaptop personal computer (PC), and in fact, may be implanted using a PCthat has been appropriately configured to include adirectional-programming device and programmed to perform the functionsdescribed herein. Alternatively, the CP 18 may take the form of amini-computer, personal digital assistant (PDA), smartphone, etc., oreven a remote control (RC) with expanded functionality. Thus, theprogramming methodologies can be performed by executing softwareinstructions contained within the CP 18. Alternatively, such programmingmethodologies can be performed using firmware or hardware. In any event,the CP 18 may actively control the characteristics of the electricalstimulation generated by the IPG 14 to allow the optimum stimulationparameters to be determined based on patient response and feedback andfor subsequently programming the IPG 14 with the optimum stimulationparameters.

To allow the user to perform these functions, the CP 18 includes a mouse72, a keyboard 74, and a programming display screen 76 housed in a case78. It is to be understood that in addition to, or in lieu of, the mouse72, other directional programming devices may be used, such as atrackball, touchpad, joystick, or directional keys included as part ofthe keys associated with the keyboard 74. In the illustrated embodiment,the monitor 76 is a conventional screen. Alternatively, instead of beingconventional, the monitor 76 may be a digitizer screen, such astouchscreen (not shown), and may be used in conjunction with an activeor passive digitizer stylus/finger touch.

As shown in FIG. 7, the CP 18 further includes a control circuitry 80(e.g., a central processor unit (CPU)) and memory 82 that stores astimulation programming package 84, which can be executed by the controlcircuitry 80 to allow the user to program the IPG 14, and RC 16. The CP18 further includes output circuitry 86 (e.g., via the telemetrycircuitry of the RC 16) for downloading stimulation parameters to theIPG 14 and RC 16 and for uploading stimulation parameters already storedin the memory 66 of the RC 16, via the telemetry circuitry 68 of the RC16.

Execution of the programming package 84 by the control circuitry 80provides a multitude of display screens (not shown) that can benavigated through via use of the mouse 72. These display screens allowthe clinician to, among other functions, to select or enter patientprofile information (e.g., name, birth date, patient identification,physician, diagnosis, and address), enter procedure information (e.g.,programming/follow-up, implant trial system, implant IPG, implant IPGand lead(s), replace IPG, replace IPG and leads, replace or reviseleads, explant, etc.), generate a pain map of the patient, define theconfiguration and orientation of the leads, initiate and control theelectrical stimulation energy output by the leads 12, and select andprogram the IPG 14 with stimulation parameters in both a surgicalsetting and a clinical setting. Further details discussing theabove-described CP functions are disclosed in U.S. patent applicationSer. No. 12/501,282, entitled “System and Method for Converting TissueStimulation Programs in a Format Usable by an Electrical CurrentSteering Navigator,” and U.S. patent application Ser. No. 12/614,942,entitled “System and Method for Determining Appropriate Steering Tablesfor Distributing Stimulation Energy Among Multiple NeurostimulationElectrodes,” which are expressly incorporated herein by reference.

Most pertinent to the present inventions, execution of the programmingpackage 84 provides a user interface that conveniently allows a user toprogram the IPG 14 in a manner that emulates an ideal multipole, such asa bipole or tripole, much like in the manner described in U.S. Pat. No.8,412,345, which was previously incorporated herein by reference.However, in this case, the programming package 84 provides a series ofdifferent ideal multipole configurations that can be used to steerelectrical current relative to the electrodes 12 in response todirectional control signals generated in response to manipulation of adirectional programming device, such as one or more of the directionalprogramming devices described above.

With reference first to FIG. 8, a programming screen 100 can begenerated by the CP 16. The programming screen 100 allows a user toperform stimulation parameter testing. To this end, the programmingscreen 100 comprises a stimulation on/off control 102 that can bealternately clicked to turn the stimulation on or off. The programmingscreen 100 further includes various stimulation parameter controls thatcan be operated by the user to manually adjust stimulation parameters.In particular, the programming screen 100 includes a pulse widthadjustment control 104 (expressed in microseconds (μs)), a pulse rateadjustment control 106 (expressed in pulses per second (pps), and apulse amplitude adjustment control 108 (expressed in milliamperes (mA)).Each control includes a first arrow that can be clicked to decrease thevalue of the respective stimulation parameter and a second arrow thatcan be clicked to increase the value of the respective stimulationparameter. The programming screen 100 also includes multipolar/monopolarstimulation selection control 110, which includes check boxes that canbe alternately clicked by the user to provide multipolar or monopolarstimulation. In an optional embodiment, the case 40 of the IPG 14 may betreated as one of the lead electrodes 26, such that both the caseelectrode 40 and at least one of the lead electrodes 26 can be used toconvey anodic electrical current at the same time. Additionally, thecase electrode may be configured with all the programmability of a leadelectrode, with full anodic and cathodic fractionalization.

The programming screen 100 also includes an electrode combinationcontrol 112 having arrows that can be clicked by the user to select oneof four different electrode combinations 1-4. Each of the electrodecombinations 1-4 can be created using a variety of control elements.

The programming screen 100 also includes a set of axial steering controlelements 116 and a set of transverse steering control elements 118. Inthe illustrated embodiments, the control elements 116, 118, as well asthe other control elements discussed herein, are implemented as agraphical icon that can be clicked with a mouse or touched with a fingerin the case of a touchscreen. Alternatively, the control elementsdescribed herein may be implemented as a joy stick, touchpad, buttonpad, group of keyboard arrow keys, mouse, roller ball tracking device,horizontal or vertical rocker-type arm switches, etc., that can bepressed or otherwise moved to actuate the control elements.

When any of the axial steering control elements 116 is actuated, controlsignals are generated in response to which the control circuitry 80 isconfigured for generating stimulation parameter sets designed to axiallydisplace the locus of the electrical stimulation field (and thus, thevolume of activation (VOA)) relative to the axis of the lead 12.Likewise, when any of the transverse steering control elements 118 isactuated, control signals are generated in response to which the controlcircuitry 80 is configured for generating stimulation parameter setsdesigned to transversely displace the locus of the electricalstimulation field (and thus, the VOA) relative to the axis of the lead12.

The control elements 116, 118 may be continually actuated (i.e., bycontinuously actuating one of the control elements 116, 118, e.g., byclicking on one of the control elements 116, 118 and holding the click(i.e., continuous actuation of the control following the initial“click”), or repeatedly actuating one of the control elements 116, 118,e.g., by repeatedly clicking and releasing one of the control elements116, 118) to generate a series of control signals in response to whichthe control circuitry 80 is configured for generating the plurality ofstimulation parameter sets. The output telemetry circuitry 86 isconfigured for transmitting these stimulation parameters sets to the IPG14.

Preferably, the control signals that are generated in response to theactuation of the control elements 116, 118 or the alternative controlelements are directional, meaning that the locus of the electricalstimulation field will be displaced in a defined direction in responseto a continual actuation of a single control element irrespective of thecurrent position of the locus electrical stimulation field locus. Aswill be described in further detail below, the control circuitry 80, inresponse to the actuation of the control elements 116, 118, firstdefines a series of ideal multipoles, and computationally determines thestimulation parameters, including the fractionalized current values oneach of the electrodes, in a manner that emulates these idealmultipoles.

Each of the sets of control elements 116, 118 takes the form of a doublearrow (i.e., two oppositely pointing control element arrows) that can beactuated to modify the electrical stimulation field depending on themode of operation. For example, an upper arrow control element 116 a canbe clicked to axially displace (i.e., along the axis of the lead 12) thelocus of the electrical stimulation field in the proximal direction; alower arrow control element 116 b can be clicked to axially displace(i.e., along the axis of the lead 12) the locus of the electricalstimulation field in the distal direction; a left arrow control element118 a can be clicked to transversely displace (i.e., perpendicular tothe axis of the lead 12) the locus of the electrical stimulation fieldin the leftward direction; and a right arrow control element 118 b canbe clicked to transversely displace (i.e., perpendicular to the axis ofthe lead 12) the locus of the electrical stimulation field in therightward direction. The control elements 116, 118 also includeindicators 116 c, 118 c for displaying an indication of the locus of theelectrical stimulation field relative to the lead 12. In particular, anindicator 116 c displays a dot representative of the axial displacementof the electrical stimulation field locus, and an indicator 118 cdisplays a dot representative of the transverse displacement of theelectrical stimulation field locus.

Although the programming screen 100 illustrates a surgical paddle lead,it should be appreciated that the programming screen 100 may illustrateone or more percutaneous to either arrange the electrodes 12 in an axialdirection (in the case of a single neurostimulation lead) and allowingthe electrical current to be steering in an axial direction, orarranging the electrodes 12 in two dimensions (in the case of multipleneurostimulation leads), thereby arranging the electrodes in twodimensions and allowing the electrical current to be steered in twodimensions much like the surgical paddle lead. Of course, the electrodescan be arranged in three-dimensions (e.g., by arranging threeneurostimulation leads in three-dimensions or by using electrodes on asingle neurostimulation lead that are arranged in three-dimensions,e.g., the segmented neurostimulation leads described in U.S. ProvisionalPatent Application Ser. No. 61/374,879), in which case, the electricalcurrent can be steering in three-dimensions.

The programming screen 100 displays a two-dimensional graphicalrendering of the electrode array 26 relative to a graphicalrepresentation of the anatomical structure 200 that is preferably thestimulation target. Based on the current stimulation parameter set, thecontrol circuitry 80 computes an estimate of a resulting volume ofactivation VOA 202, and generates display signals that prompt themonitor 76 to display a graphical representation of the VOA 202 with thegraphical electrode array 26 and graphical anatomical structure 200. Inthe preferred embodiment, the graphical VOA 202 is superimposed over thegraphical anatomical structure 200.

The programming screen 100 also displays a graphical rendering of anideal multipole 250 that is manipulated by the control circuitry 80relative to the electrode array 26. In one embodiment, the multipole 250is a generalized multipole that defines five imaginary locations for acentral ideal pole 252 and four surrounding ideal poles 254(1)-254(4)(collectively, 254). The generalized multipole 250 is defined withseveral sets of variable values that are stored in memory 82. These setsof variable values include a set of variable values defining thepolarities of the central ideal pole 252 and surrounding ideal poles254, a set of variable values defining a spatial relationship betweenthe central ideal pole 252 and the electrode array 26, a set of variablevalues defining a spatial relationship between the surrounding idealpoles 254 and the central ideal pole 252, and a set of variable valuesdefining relative intensities of the surrounding ideal poles 254.

Referring further to FIG. 9, in accordance with typical SCS regimens,which assume that neurons are stimulated by negatively polarizedcurrent, the set of variable values defining the polarities in theillustrated embodiment, defines the polarity of the central ideal pole252 as being a cathode (“−”) and the polarities of the surrounding idealpoles 254 as being anodes (“+”). In alternative embodiments, the centralideal pole 252 may be defined as an anode (“+”) and the polarities ofthe surrounding ideal poles 254 may be defined as cathodes (“−”).Alternatively, rather than having a set of variable values that definethe polarities of the ideal poles, the polarities of the ideal poles maybe pre-defined in a fixed manner, such that they cannot be varied.

In the illustrated embodiment, the spatial relationship between thecentral ideal pole 252 and the electrode array 26 is a rectilinearposition (e.g., an x-y position in a two-dimensional coordinate system,or an x-y-z position in a three-dimensional coordinate system). Inalternative embodiments, the spatial relationship between the centralideal pole 252 and the electrode array 26 may be a position in a polarcoordinate system, cylindrical coordinate system, or sphericalcoordinate system. The spatial relationship between the central idealpole 252 and the electrode array 26 may be stored as absolute coordinatepositions for both the central ideal pole 252 and the electrode array26, or may be stored as a relative coordinate position between thecentral ideal pole 252 and the electrode array 26. The spatialrelationship between the central ideal pole 252 and the electrode array26 may be determined relative to a reference point in the electrodearray 26, e.g., a designated electrode.

In the illustrated embodiment, the spatial relationship between thesurrounding ideal poles 254 and the central ideal pole 252 comprises anabsolute distance (referred to as “focus”) between each of thesurrounding ideal poles 254 and the central ideal pole 252. Inparticular, the spatial relationship between the first ideal pole 254(1)and the central ideal pole 252 is defined by a vertical focus VF1, thespatial relationship between the second ideal pole 254(2) and thecentral ideal pole 252 is defined by a vertical focus VF2, the spatialrelationship between the third ideal pole 254(3) and the central idealpole 252 is defined by a horizontal focus HF1, and the spatialrelationship between the fourth ideal pole 254(4) and the central idealpole 252 is defined by a horizontal focus HF2.

In the illustrated embodiment, the relative intensities A1-A4 of thesurrounding ideal poles 254 are defined using fractionalized values. Forexample, each of the surrounding ideal poles 254 may have an intensityof 25%. Notably, if a specific ideal pole 254 is turned on (oractivated), it will have a non-zero intensity value, and if a specificideal pole 254 is turned off (not activated), it will have a zerointensity value. Thus, if the relative intensities A1, A2 are non-zero(ideal poles 254(1), 254(2) activated), and the relative intensities A3,A4 are zero (ideal poles 254(3), 254(4) not activated), a longitudinaltripole configuration (rostro-caudal in the case of SCS) can be formedfrom the generalized ideal multipole 250, as shown in FIG. 10. Incontrast, if the relative intensities A3, A4 are non-zero (ideal poles254(3), 254(4) activated), and the relative intensities A1, A2 are zero(ideal poles 254(1), 254(2) not activated), a transverse tripoleconfiguration (medio-lateral in the case of SCS) can be formed from thegeneralized ideal multipole 250, as shown in FIG. 11.

The ideal poles 254(1) and 254(2) and the central ideal pole 252 arealigned along a first axis 256 along which the absolute distances forthe ideal poles 254(1) and 254(2) are defined, and the ideal poles254(3) and 254(4) and the central ideal pole 252 are aligned along asecond axis 258 along which the absolute distances for the ideal poles254(3) and 254(4) are defined. In this case, a set of variable valuesdefining an angle between one or both of the axes 256, 258 and areference axis 260 may be stored in memory 82.

In the illustrated embodiment, the reference axis 260 is an axis that istransverse to the longitudinal axis of the lead 12. For example, asshown in FIG. 9, the angle α between the axis 256 and the reference axis260 is defined to be 90 degrees, essentially aligning the idealmultipole 250 with the electrode array 26. As shown in FIG. 12, theangle α between the axis 256 and the reference axis 260 is defined to be120 degrees, such that the ideal multipole 250 is rotationally offsetfrom the electrode array 26.

If the relative angle between the axes 256, 258 is fixed (i.e., the axes256, 258 cannot be rotated relative to each other), only one angle(e.g., the angle between the axis 256 and the reference axis 260) needsto be used. This may, e.g., be the case when the axes 256, 258 arealways assumed to be orthogonal to each other, as shown in FIGS. 9 and12. However, in alternative embodiments, the axes 256, 258 may berotated relative to each other, in which case, two angles need to bedefined. For example, as shown in FIG. 13, the angle α between the axis256 and the reference axis 260 is defined to be 120 degrees, and theangle β between the axis 258 and the reference axis 260 is defined to be−15 degrees. In this case, the axes 256, 258 are non-orthogonal to eachother. Alternatively, rather than defining the angles for both axes 256,258 relative to the reference axis 260, the angle of one of the axes256, 258 can be defined relative to the reference axis 260, and theangle of the other one of the axes 256, 256 can be defined relative tothe one axes. For example, the angle α between the axis 256 and thereference axis 260 can be defined to be 120 degrees, and the angle φbetween the axes 256, 258 can be defined to be 135 degrees.

In the preferred embodiment, the vertical focuses VF1, VF2 for therespective ideal poles 254(1), 254(2), and the horizontal HF1, HF2 forthe respective ideal poles 254(3), 254(4), are independently defined.For example, although in the FIG. 9 embodiment, the vertical focusesVF1, VF2 are equal (symmetrical) and the horizontal focuses HF1, HF2 areequal (symmetric), in the FIG. 13 embodiment, the vertical focuses VF1,VF2 are not equal (VF1 is greater than VF2)(asymmetric), and thehorizontal focuses HF1, HF2 are not equal (HF1 is less thanHF2)(asymmetric).

The control circuitry 80 is configured for modifying at least one of thesets of values that define the ideal multipole 250 in response to thedirectional control signals generated by the user interface. Forexample, the control circuitry 80 may modify the polarities of thecentral ideal pole 252 and surrounding ideal poles 254, the rectilinearposition of the central ideal pole 252 relative to the electrode array26, the vertical focuses VF1, VF2 and horizontal focuses HF1, HF2, thefractionalized values A1-A4 of the surrounding ideal poles 254, and/orany of the angles α, β, φ. In an optional embodiment, the controlcircuitry 80 may modify one of the sets of values that define the idealmultipole 250 as a function of an automated sequence (e.g., the sets ofvalues are modified every second), as a function of an electrodeboundary (e.g., the ideal multipole 250 must remain within a certainelectrode region), or as a function of a particular electrode position(e.g., one of the poles of the ideal multipole 250 must be affixed to aparticular electrode).

The control circuitry 80 is further configured for generating, based onthe modification, stimulation parameter values defining relativeamplitude values for the respective electrodes 12 to emulate theselected poles of the ideal multipole 250, and instructing the IPG 14 toconvey electrical energy to the electrode array 26 in accordance withthe stimulation parameter values. Further details discussing thecomputation of relative electrode amplitude values to emulate idealmultipoles are disclosed in U.S. Pat. No. 8,412,345, which waspreviously incorporated herein by reference.

Significantly, the control circuitry 80 may steer current in aparticular direction by modifying the values defining the generalizedideal multipole 250 in response to the continual generation of thedirectional control signals, and instructing the IPG 14 to convey theelectrical energy to the electrode array 26 in accordance withstimulation parameter values generated based on the modified values.

For example, the control circuitry 80 may be configured for sequentiallydefining a plurality of different ideal bipole/tripole configurationsrelative to electrode array 26 in response to the directional controlsignals.

In one embodiment shown in FIG. 14, the control circuitry 80 utilizes alongitudinal tripole configuration having a central ideal cathode 252and two flanking anodes 254(1) and 254(2) as a basis for defining thedifferent ideal bipole/tripole configurations. The longitudinal tripoleconfiguration can be derived from the generalized ideal multipole 250 bydefining the polarization of the central ideal pole 252 to be a cathodeand the polarizations of the surrounding ideal poles 254 to be anodes,defining the intensity values for the ideal poles 254(1) and 254(2) tobe non-zero values, and defining the intensity values for the idealpoles 254(3) and 254(4) (not shown in FIG. 14) to be zero values. Thecharacteristics of the basis longitudinal tripole configuration can bedefined by a longitudinal focus (LGF) (equivalent to the vertical focus(VF1) of the generalized multipole 250), an upper anode percentage(UAP)(equivalent to the intensity value A1 of the generalized multipole250), and the cathode position relative to the electrode array 26. Thelower anode percentage can be computed in accordance with the equationA2=100−A1.

The control circuitry 80 may sequentially define the different idealbipole/tripole configurations in accordance with a weaving currentsteering technique. For example, a series of ideal bipole/tripoleconfigurations are illustrated in FIG. 15 over a plurality of dashedlines representing available electrode positions in the electrode array26. As shown, the individual poles of the ideal bipole/tripoleconfigurations are generally maintained as much as possible over anavailable electrode position in order to emulate the idealbipole/tripole configurations in the most energy efficient manner. Inthe illustrated embodiment, all of the ideal tripole configurations aresymmetrical in that the ideal anodes are equally spaced from the centralideal cathode. Each illustrated bipole/tripole configuration has adesignator indicating whether it is a tripole or bipole (T for tripoleand B for bipole), a subscripted designator indicating the longitudinalfocus (LGF) in terms of electrode separation, and, in the case of abipole, a subscripted designator indicating the bipole is an upperbipole (u), meaning that the anode is above the cathode, or the bipoleis a lower bipole (1), meanng that the anode is below the cathode.

In the embodiment illustrated in FIG. 15, the different idealbipole/tripole configurations are sequentially defined in the followingorder: a narrow ideal tripole configuration (T₂), a narrow upper idealbipole configuration (B_(2u)), a wide upper ideal bipole configuration(B_(3u)), a wide ideal tripole configuration (T_(2.5)), a wide lowerideal bipole configuration (B_(3l)), a narrow lower ideal bipoleconfiguration (B_(2l)), and the narrow ideal tripole configuration (T₂).For purposes of this specification, the terms “narrow” and “wide,” whenused together to define an ideal bipole or an ideal tripole, arerelative terms, and simply mean that the narrow bipole and/or narrowtripole have longitudinal focuses (LGFs) that are less than thelongitudinal focuses (LGFs) of the wide bipole and/or wide tripole.

The ideal bipole/tripole configurations illustrated in FIG. 15 may beconsidered critical points between which the cathode position andlongitudinal focus (LGF) are incrementally changed by mapping thesequences in a “weave space,” defined by the longitudinal focus (LGF)and the upper anode percentage (UAP). As best shown in FIG. 16, thesequence of ideal bipole/tripole configurations is defined by atrajectory line sequentially connecting the critical points(representing by circles) that provides a continuous change in the idealbipole/tripole configurations.

As can be seen from FIG. 16, the sequence beginning with the narrowideal tripole configuration (T₂) and ending with the narrow upper idealbipole configuration (B_(2u)) incrementally increases the upper anodepercentage (UAP) while maintaining the longitudinal focus (LGF). Thesequence beginning with the narrow upper ideal bipole configuration(B_(2u)) and ending with the wide upper ideal bipole configuration(B_(3u)) maintains the upper anode percentage (UAP) while incrementallyincreasing the longitudinal focus (LGF). The sequence beginning with thewide upper ideal bipole configuration (B_(3u)) and ending with the wideideal tripole configuration (T_(2.5)) incrementally decreases the upperanode percentage (UAP) while incrementally decreasing the longitudinalfocus (LGF). The sequence beginning with the wide ideal tripoleconfiguration (T_(2.5)) and ending with the wide lower ideal bipoleconfiguration (B_(3l)) incrementally decreases the upper anodepercentage (UAP) while incrementally increasing the longitudinal focus(LGF). The sequence beginning with the wide lower ideal bipoleconfiguration (B_(3l)) and ending with the narrow lower ideal bipoleconfiguration (B_(2l)) maintains the upper anode percentage (UAP) whileincrementally decreasing the longitudinal focus (LGF). The sequencebeginning with the narrow lower ideal bipole configuration (B_(2l)) andending with the narrow ideal tripole configuration (T₂) incrementallyincreases the upper anode percentage (UAP) while maintaining thelongitudinal focus (LGF).

Notably, the above-mentioned sequence maintains the same position of theideal cathode relative to the electrode array 26 while transitioningthrough different types of ideal bipole/tripole configurations betweenthe narrow ideal tripole configuration (T₂) and the wide upper idealbipole configuration (B_(3u)), incrementally changes the position of theideal cathode relative to the electrode array 26 in one direction (inthis case, upward) between the wide upper ideal bipole configuration(B_(3u)) and the wide lower ideal bipole configuration (B_(3l)), and themaintains the same position of the ideal cathode relative to theelectrode array 26 while transitioning through different types of idealbipole/tripole configurations between the wide lower ideal bipoleconfiguration (B_(3l)) and the narrow ideal tripole configuration (T₂).

The sequence illustrated in FIG. 15 can be repeatedly cycled through,with the effect being that the ideal cathode is shifted upward by oneelectrode per each cycle. When electrical energy is conveyed to theelectrode array 26 in accordance with stimulation parameter setscomputed to emulate the sequence of bipolar/tripole configurations, avolume of activation (VOA) will be incrementally displaced along thetissue of the patient in concordance with the incremental displacementof the ideal cathode. If each ideal bipole/tripole configuration isgenerally aligned along the spinal cord of the patient, the VOA will berostro-caudally displaced along the spinal cord of the patient.

Notably, different step sizes may be used transition between the idealbipole/tripole configurations. For example, as shown in FIG. 17, a fineresolution (10 steps per critical point transition) are used totransition between the critical points where the cathode is not beingshifted, and an even finer resolution (20 steps per critical pointtransition) are used to transition between the critical points where thecathode is being shifted. As shown in FIG. 18, a coarse resolution (5steps per critical point transition) is used to transition between allof the critical points.

It should be appreciated that the different ideal bipole/tripoleconfigurations may be sequentially defined in a different order andshift the cathode using different ones of the bipole/tripoleconfigurations as compared to the sequence illustrated in FIG. 15. Forexample, as shown in FIG. 19, the different ideal bipole/tripoleconfigurations may be defined in the following order: a narrow upperideal bipole configuration (B_(2u)), a wide upper ideal bipoleconfiguration (B_(3u)), a wide ideal tripole configuration (T₃), a widelower ideal bipole configuration (B_(3l)), a narrow lower ideal bipoleconfiguration (B_(2l)), a narrow ideal tripole configuration (T_(2.5)),and the narrow upper ideal bipole configuration (B_(2u)).

As best shown in FIG. 20, the sequence of ideal bipole/tripoleconfigurations is defined by a trajectory line sequentially connectingthe critical points (representing by circles). As can be seen, thesequence beginning with the narrow upper ideal bipole configuration(B_(2u)) and ending with the wide upper ideal bipole configuration(B_(3u)) maintains the upper anode percentage (UAP) while incrementallyincreasing the longitudinal focus (LGF). The sequence beginning with thewide upper ideal bipole configuration (B_(3u)) and ending with the wideideal tripole configuration (T₃) incrementally decreases the upper anodepercentage (UAP) while maintaining the longitudinal focus (LGF). Thesequence beginning with the wide ideal tripole configuration (T₃) andending with the wide lower bipole configuration (B_(3l)) incrementallydecreases the upper anode percentage (UAP) while maintaining thelongitudinal focus (LGF). The sequence beginning with the wide lowerideal bipole configuration (B_(3l)) and ending with the narrow lowerideal bipole configuration (B_(2l)) maintains the upper anode percentage(UAP) while incrementally decreasing the longitudinal focus (LGF). Thesequence beginning with the narrow lower ideal bipole configuration(B_(2l)) and ending with the narrow ideal tripole configuration(T_(2.5)) incrementally increases the upper anode percentage (UAP) whileincrementally increasing the longitudinal focus (LGF). The sequencebeginning with the narrow ideal tripole configuration (T_(2.5)) andending with the narrow upper ideal bipole configuration (B_(2u))incrementally increases the upper anode percentage (UAP) whileincrementally decreasing the longitudinal focus (LGF).

Notably, the above-mentioned sequence maintains the same position of theideal cathode relative to the electrode array 26 while transitioningthrough different types of ideal bipole/tripole configurations betweenthe narrow upper ideal bipole configuration (B_(2u)) and the narrowlower ideal bipole configuration (B_(2l)), and incrementally changes theposition of the ideal cathode relative to the electrode array 26 in onedirection (in this case, upward) between the narrow lower ideal bipoleconfiguration (B_(2l)) and the narrow upper ideal bipole configuration(B_(2u)).

The sequence illustrated in FIG. 19 can be repeatedly cycled through,with the effect being that the ideal cathode is shifted upward by oneelectrode per each cycle. As discussed above with respect to FIG. 15, ifeach of ideal bipole/tripole configuration is generally aligned alongthe spinal cord of the patient, when electrical energy is conveyed tothe electrode array 26 in accordance with stimulation parameter setscomputed to emulate the sequence of bipolar/tripole configurations, avolume of activation (VOA) will be incrementally rostro-caudallydisplaced along the spinal cord of the patient in concordance with theincremental displacement of the ideal cathode.

Although the cathode and anodes of the tripole configurations arealigned along an axis, as illustrated in FIGS. 15 and 19, it should beappreciated that the cathode and anodes may be misaligned along theaxis. For example, in the manner illustrated in FIG. 13, the controlcircuitry 80 may define the angles α and β in a manner that the idealpoles 254(1) and 254(2) and central ideal pole 252 are misaligned alongthe axis 256.

Rather than sequentially defining different ideal bipole/tripoleconfigurations that are aligned in the same direction, in response tothe directional control signals, the control circuitry 80 may beconfigured for sequentially defining a plurality of different idealmultipole configurations, some of which may be orthogonal to each other.

In one embodiment shown in FIG. 21, the control circuitry 80 utilizes ageneralized ideal multipole 300 having a central ideal cathode 352 andfour surrounding ideal anodes 354 as a basis for defining the orthogonalmultipole configurations. The generalized ideal multipole 300 can bederived from the generalized ideal multipole 250 by defining thepolarization of the central ideal pole 252 to be a cathode and thepolarizations of the surrounding ideal poles 254 to be anodes. Thevertical focuses VF1, VF2 of the generalized ideal multipole 250 havebeen respectively replaced with an above anode focus AF and a belowanode focus BF, and the horizontal focuses HF1, HF2 of the generalizedideal multipole 250 have been respectively replaced with a left anodefocus LF and a right anode focus RF.

With reference to FIGS. 22a-22c , a series of active electrodecombinations using the electrode array 26 of FIG. 3 can be generated toshift a volume of activation (VOA) from a medial to a lateral location.As will be described in further detail below, the ideal multipoles canbe generated to match the actual sequence of active electrodecombinations.

The sequence of active electrode combinations may begin with atransverse tripole electrode arrangement S1 created by activating themiddle row in the inner electrode columns 26′ (electrodes E9, E14) ascathodes, and activating the two flanking electrodes in the left outercolumn 26″ (electrodes E3, E4) and the two flanking electrodes in theright outer column 26″ (electrodes E19, E20) as anodes, thereby creatinga medial-lateral electrical field that effectively places the VOA in amedial position relative to the electrode array 26. This transversetripole arrangement provides high selectivity for DC nerve fibers overDR nerve fibers.

Another transverse tripole electrode arrangement S2 is created by usingthe same transverse tripole electrode arrangement S1, but deactivatingthe electrode in the left inner electrode column 26′ (electrode E9),thereby creating a medial-lateral electrical field that laterally shiftsthe resulting VOA to the right from the medial position.

A narrow longitudinal tripole electrode arrangement S3 is created byactivating the middle electrode in the right inner electrode column 26′(electrode E14) as a cathode, and activating two flanking electrodes inthe right inner electrode column 26′ (electrodes E12, E16) as anodes,thereby creating a rostral-caudal electrical field that shifts theresulting VOA further to the right.

A wide longitudinal tripole electrode arrangement S4 is created byactivating the middle two electrodes in the right outer electrode column26′ (electrodes E19, E20), and activating two flanking electrodes in theright outer electrode column 26′ (electrodes E17, E22), thereby creatinga rostral-caudal electrical field that shifts the resulting VOA all theway to the right.

A quadpole electrode arrangement S5 is created by using the longitudinaltripole electrode arrangement S4, but activating the middle electrode inthe right inner electrode column 26′ (electrode E14).

Notably, although displacement of the resulting VOA is shown to occurfrom the medial location to the right, it can be appreciated that theresulting VOA can be displaced from the medial location to the left

As illustrated in FIG. 22b , the control circuitry 50 may sequentiallydefine ideal multipole configurations that respectively match the activeelectrode arrangements illustrated in FIG. 22a . In particular, thecontrol circuitry 50 may define the ideal multipole configurations inthe following order: a first ideal tripole configuration S1 oriented ina first direction (transverse), a second ideal tripole configuration S2oriented in the first direction (transverse), a third ideal tripoleconfiguration S3 oriented in a second orthogonal direction(longitudinal), a fourth ideal tripole configuration S4 oriented in thesecond direction (longitudinal), and an ideal quadpole configuration S5.

Referring further to FIG. 22c , the control circuitry 50 defines thedifferent multipole configurations in accordance with the anodeintensities (A1-A4), anode focuses (AF, BF, LF, RF), and position of thecentral ideal cathode relative to the electrode array 26.

In particular, the first ideal tripole configuration S1 can be definedas a narrow, transverse, symmetrical ideal tripole configuration bysetting the anode intensities A1, A2 to zero values, setting the anodeintensities A3, A4 to non-zero values, and setting the left and rightanode focuses LF, RF to relatively small equal values, and defining therelative position between the central ideal cathode and the electrodearray 26, such that the central ideal cathode is transversely alignedbetween the two inner electrode columns 26′.

The second ideal tripole configuration S2 can be defined as a narrow,transverse, asymmetrical ideal tripole configuration by setting theanode intensities A1, A2 to zero values, setting the anode intensitiesA3, A4 to non-zero values, setting the left anode focus LF to be arelative large value, setting the right anode focus RF to be arelatively small value, and defining the relative position between thecentral ideal cathode and the electrode array 26, such that the centralideal cathode is transversely aligned with the right inner electrodecolumn 26′.

The third ideal tripole configuration S3 can be defined as a narrow,longitudinal, symmetrical ideal tripole configuration by setting theanode intensities A1, A2 to non-zero values, setting the anodeintensities A3, A4 to zero values, setting the above and below anodefocuses AF, BF to relatively small equal values, and defining therelative position between the central ideal cathode and the electrodearray 26, such that the central ideal cathode is transversely alignedwith the right inner electrode column 26′.

The fourth ideal tripole configuration S4 can be defined as a widesymmetrical ideal tripole configuration by setting the anode intensitiesA1, A2 to non-zero values, setting the anode intensities A3, A4 to zerovalues, setting the above and below anode focuses AF, BF to relativelylarge equal values, and defining the relative position between thecentral ideal cathode and the electrode array 26, such that the centralideal cathode is transversely aligned with the right outer electrodecolumn 12.

The ideal quadpole configuration S5 can be defined to have two idealanodes that longitudinally flank the central ideal cathode, and a thirdideal anode positioned to the left of the central ideal cathodeequidistantly from the two anodes by setting the anode intensities A1,A2, A3 to non-zero values, setting the anode intensity A4 to a zerovalue, setting the above and below anode focuses AF, BF to relativelylarge equal values, setting the left anode focus LF to a relativelysmall value, and defining the relative position between the centralideal cathode and the electrode array 26, such that the central idealcathode is transversely aligned with the right inner electrode column26′.

The ideal multipole configurations illustrated in FIG. 22b may beconsidered critical points between which the anode intensities (A1-A4),anode focuses (LF, RF, AF, BF), and the cathode advancement areincrementally changed to smoothly advance the VOA from a medial positionto a lateral position, as best shown in FIG. 22 c.

In particular, between the first ideal tripole configuration S1 and thesecond ideal tripole configuration S2, the above and below anodeintensities A1, A2 are maintained at zero values (remain turned off),the left and right anode intensities A3, A4 are maintained at non-zerovalues (remain turned on), the left anode focus LF is incrementallyincreased to a relatively high value while the right anode focus RF isincrementally decreased to a relatively low value, and the position ofthe ideal central cathode is incrementally shifted to the right.

Between the second ideal tripole configuration S2 and the third idealtripole configuration S3, the above and below anode intensities A1, A2are incrementally increased from the zero values (gradually turned on)while the left and right anode intensities A3, A4 are incrementallydecreased to zero values (gradually turned off), the left and rightanode focuses LF, RF are maintained, and the position of the idealcentral cathode is maintained.

Between the third ideal tripole configuration S3 and the fourth idealtripole configuration S4, the non-zero values of the above and belowanode intensities A1, A2 are maintained (remain turned on), the zerovalues of the left and right anode intensities A3, A4 are maintained(remain turned off), the left anode focus LF is incrementally decreasedwhile the right anode focus RF is incrementally increased, the above andbelow anode focuses AF, BF are incrementally increased, and the positionof the ideal central cathode is incrementally shifted to the right.

Between the fourth ideal tripole configuration S4 and the ideal quadpoleconfiguration S5, the above and below anode intensities A1, A2 areincrementally decreased to lesser non-zero values (gradually turneddown, e.g., by 5-50%), the left anode intensity A3 is incrementallyincreased from the non-zero value (gradually turned up, e.g., by10-100%), the zero value of the right anode intensity A4 is maintained(remained turned off), all the anode focuses AF, BF, LF, RF aremaintained, and the position of the ideal central cathode is maintained.

When electrical energy is conveyed to the electrode array 26 inaccordance with stimulation parameter sets computed to emulate thesequence of ideal tripole configurations and quadpole configuration, avolume of activation (VOA) will be incrementally displacedmedio-laterally across the spinal cord of the patient in concordancewith the incremental displacement of the ideal cathode.

It should be appreciated that it is important that, during the currentsteering methodologies described with respect to FIGS. 14-22, none ofthe poles of the ideal multipole configurations is outside of themaximum extent of the electrode array 26.

For example, if the surgical paddle lead 12 illustrated in FIG. 3 isconventionally implanted within the patient such that the electrodecolumns are aligned with the longitudinal axis of the spinal cord, it isimportant that an ideal pole not extend above electrodes E1 and E17(which may occur when current is steered in the rostral direction), notextend below electrodes E6 and E22 (which may occur when current issteered in the caudal direction), not extent to the left of the leftelectrode column 26″ (which may occur when current is steered in thelateral direction to the left), and not extend to the right of the rightelectrode column 26″ (which may occur when current is steered in thelateral direction to the right). If the percutaneous leads 12illustrated in FIG. 4 are implanted with the patient such that the leadsare aligned with the longitudinal axis of the spinal cord and the distalends of the leads are pointed in the rostral direction (as shown in FIG.2), it is important that an ideal pole not extend above electrodes E1and E9 (which may occur when current is steered in the rostraldirection), and not extend below electrodes E8 and E16 (which may occurwhen current is steered in the caudal direction). It can be appreciatedfrom this that, in the case of a linear electrode array (e.g., any ofthe electrode columns of the surgical paddle lead or percutaneousleads), the maximum extent will be coincident with an electrode 26 atthe end of the linear electrode array (e.g., for the surgical paddlelead 12, electrodes E1 and E6 for the left outer electrode column 26″,electrodes E7 and E11 for the left inner electrode column 26′,electrodes E12 and E16 for the right inner electrode column 26′, andelectrodes E17 and E22 for the right outer electrode column 26″; andelectrodes E1 and E8 for the percutaneous lead 12(1); and electrodes E9and E16 for the percutaneous lead 12(2)).

Referring to FIG. 23, to prevent any ideal pole from extending outsidethe maximum extent of the electrode array 26, the control circuitry 50first sequentially defines a plurality of ideal multipole configurationsrelative to the electrode array 26; e.g., in the manner described abovewith respect to FIG. 15. The control circuitry 50 then determines aspatial relationship between at least one of the defined plurality ofideal multipole configurations and the maximum extent of the electrodearray 26, and if any pole of a defined ideal multipole configurationwill spatially exceed the maximum extent of the electrode array 26, thecontrol circuitry 50 modifies the plurality of ideal multipoleconfigurations such that all of the defined ideal multipoleconfigurations that spatially exceeded the maximum extent of theelectrode array 26 will spatially be within the maximum extent of theelectrode array 26. As can be seen from FIG. 23, if the defined idealmultipole configurations remain unmodified, the upper pole (anode) ofthe wide upper ideal bipole configuration B_(3u) and the upper pole(anode) of the wide ideal bipole configuration T_(2.5) extend above therostral-most electrode (i.e., the maximum allowed rostral focus). Asshown in FIG. 24, the sequence of ideal bipole/tripole configurations isdefined by the dashed trajectory line sequentially connecting thecritical points (representing by circles).

The control circuitry 50 corrects this by decreasing the longitudinalfocus LGF of the wide upper ideal bipole configuration B_(3u)(essentially eliminating the wide upper ideal bipole configurationB_(3u) and replacing it with a narrower upper ideal bipole configurationB_(2.5u)). The control circuitry 50 also delays the initial rostraldisplacement of the ideal cathode, which was previously to occur at thewide upper ideal bipole configuration B_(3u), until the wide idealtripole configuration T_(2.5). To provide another step for displacingthe ideal cathode before the final displacement at the wide lower idealbipole configuration B_(3l), the control circuitry 50 adds a lower idealbipole configuration B_(2.5l) between the wide ideal tripoleconfiguration T_(2.5) and the wide lower ideal bipole configurationB_(3l).

As best shown in FIG. 25, the sequence of ideal bipole/tripoleconfigurations is defined by a trajectory line sequentially connectingthe critical points (representing by circles). As can be seen, thesequence beginning with the narrow ideal tripole configuration (T₂) andending with the narrow upper ideal bipole configuration (B_(2u))incrementally increases the upper anode percentage (UAP) whilemaintaining the longitudinal focus (LGF). The sequence beginning withthe narrow upper ideal bipole configuration (B_(2u)) and ending with the(adjusted) wide upper ideal bipole configuration (B_(2.5u)) maintainsthe upper anode percentage (UAP) while incrementally increasing thelongitudinal focus (LGF). The sequence beginning with the wide upperideal bipole configuration (B_(2.5u)) and ending with the wide idealtripole configuration (T_(2.5)) incrementally decreases the upper anodepercentage (UAP) while incrementally decreasing the longitudinal focus(LGF). The sequence beginning with the wide ideal tripole configuration(T_(2.5)) and ending with the (adjusted) wide lower ideal bipoleconfiguration (B_(2.5l)) incrementally decreases the upper anodepercentage (UAP) while maintaining the longitudinal focus (LGF). Thesequence beginning with the wide lower ideal bipole configuration(B_(2.5l)) and ending with the wide lower ideal bipole configuration(B_(3l)) maintains the upper anode percentage (UAP) while incrementallyincreasing the longitudinal focus (LGF). The sequence beginning with thewide lower ideal bipole configuration (B_(3l)) and ending with thenarrow lower ideal bipole configuration (B_(2l)) maintains the upperanode percentage (UAP) while incrementally decreasing the longitudinalfocus (LGF).

Notably, the above-mentioned sequence maintains the same position of theideal cathode relative to the electrode array 26 while transitioningthrough different types of ideal bipole/tripole configurations betweenthe narrow ideal tripole configuration (T₂) and the wide ideal tripoleconfiguration (T_(2.5)) and between the wide lower ideal bipoleconfiguration (B_(3l)) and the narrow lower ideal bipole configuration(B_(2l)), and incrementally changes the position of the ideal cathoderelative to the electrode array 26 in one direction (in this case,upward) between the wide ideal tripole configuration (T_(2.5u)) and thewide lower ideal bipole configuration (B_(3l)).

The sequence illustrated in FIG. 24 can be repeatedly cycled through,with the effect being that the ideal cathode is shifted upward by oneelectrode per each cycle. As discussed above with respect to FIG. 15, ifeach of ideal bipole/tripole configuration is generally aligned alongthe spinal cord of the patient, when electrical energy is conveyed tothe electrode array 26 in accordance with stimulation parameter setscomputed to emulate the sequence of bipolar/tripole configurations, avolume of activation (VOA) will be incrementally rostro-caudallydisplaced along the spinal cord of the patient in concordance with theincremental displacement of the ideal cathode.

As can be appreciated, by modifying the longitudinal focus (LGF), thecontrol circuitry 50 displaces the ideal anode(s) and ideal cathoderelative to each other for the respective ideal multipoleconfigurations. In doing this, values defining a spatial relationshipbetween the ideal anode(s) and ideal cathode (in this case, thelongitudinal focus (LGF)) may be stored in memory. At least some ofthese values may be variable, such that the control circuitry 50 maydisplace the ideal anode(s) and ideal cathode relative to each other bymodifying the variable values.

For example, as illustrated in FIG. 26, seven critical points (P 1-P7)representing seven ideal bipole/tripole configurations at any given timeare shown in a weave space, defined by the longitudinal focus (LGF) andthe upper anode percentage (UAP), with the sequence of idealbipole/tripole configurations defined by a trajectory line sequentiallyconnecting the critical points (representing by circles). Criticalpoints P1 and P7, which represent narrow ideal bipole/tripoleconfigurations, cannot be varied, and therefore, can be defined by fixedvalues stored in memory, and critical points P2-P6, which represent wideideal bipole/tripole configurations, can be varied, and therefore, canbe defined by variable values stored in memory.

In the illustrated embodiment, critical points P1, P7 initiallyrepresent a narrow lower ideal bipole configuration and a narrow upperideal bipole configuration; critical points P2, P3 initially representidentical wide upper ideal bipole configurations, critical point P4initially represents a wide ideal tripole configuration, and criticalpoints P5, P6 initially represent identical wide lower ideal bipoleconfigurations. Initially, it is assumed that the maximum longitudinalfocus (LGF) in both the rostral and caudal direction is above a certainlimit. The control circuitry 50 may change the variable valuesassociated with critical points P2-P6, such that no pole of an idealbipole/tripole configuration exceeds the maximum longitudinal focus(LGF) (i.e., the maximum extent of the electrode array 26). In theillustrated embodiment, the variable values associated with criticalpoints.

For example, if the maximum longitudinal focus at issue is a rostrallongitudinal focus (i.e., the upper poles of the ideal bipole/tripoleconfigurations may possibly exceed the upper maximum extent of theelectrode array 26), critical points P2, P5 may be displacedhorizontally left along the respective P2, P5 moving lines (therebydecreasing the respective longitudinal focus values (LGFs), and thecritical point P3, P4 may be displaced diagonally left and downwardalong the respective P3, P4 moving lines (thereby decreasing therespective longitudinal focus values (LGFs) and decreasing the upperanode percentages (UAPs), as shown in FIG. 27 a.

When the rostral maximum longitudinal focus (LGF) is less than thelongitudinal focus (LGF) of critical point P2, critical points P2, P5are concurrently displaced along the respective P2, P5 moving lines tothe same longitudinal focus (LGF) value (thereby effectively narrowingthe wide upper and lower ideal bipole configurations), and criticalpoint P3 is displaced along the P3 moving line (effectively changing theupper ideal bipole configuration into a narrower ideal tripoleconfiguration). If the rostral maximum longitudinal focus (LGF) is lessthan the longitudinal focus (LGF) of critical point P4, critical pointP4 is displaced along the P4 moving line (effectively narrowing the wideideal tripole configuration). In this case, the critical points P3, P4are concurrently displaced along the respective P3, P4 moving lines tothe same longitudinal focus (LGF) value and the same upper anodepercentage (UAP) value. In effect, the critical points P3, P4 willrepresent the identical ideal tripole configuration.

As shown in FIG. 27b , critical points P2, P3, P5 are displaced inaccordance with three different rostral maximum longitudinal focuses(LGFs) (represented by vertical solid lines) that are between thelongitudinal focuses (LGFs) of critical points P2, P4. As shown in FIG.27c , critical points P2, P3, P4, P5 are displaced in accordance withtwo different rostral maximum longitudinal focuses (LGFs) (representedby vertical solid lines) that are less than the longitudinal focus (LGF)of critical point P4. Shifting of the ideal cathode may be appliedbetween critical points P3, P6. A modified weaving trajectory linesequentially connects the modified critical points P1-P7 shown in FIGS.27b and 27 c.

As another example, if the maximum longitudinal focus at issue is acaudal longitudinal focus (i.e., the lower poles of the idealbipole/tripole configurations may possibly exceed the lower maximumextent of the electrode array 26), critical points P3, P6 may bedisplaced horizontally left along the respective P3, P6 moving lines(thereby decreasing the respective longitudinal focus values (LGFs) anddecreasing the respective upper anode percentages (UAPs), and thecritical point P4, P5 may be displaced diagonally left and upward alongthe respective P4, P5 moving lines (thereby decreasing the respectivelongitudinal focus values (LGFs) and increasing the respective upperanode percentages (UAPs), as shown in FIG. 28 a.

When the caudal maximum longitudinal focus (LGF) is less than thelongitudinal focus (LGF) of critical point P6, critical points P3, P6are concurrently displaced along the respective P3, P6 moving lines tothe same longitudinal focus (LGF) value (thereby effectively narrowingthe wide upper and lower ideal bipole configurations), and criticalpoint P5 is displaced along the P5 moving line (effectively changing thelower ideal bipole configuration into a narrower ideal tripoleconfiguration). If the rostral maximum longitudinal focus (LGF) is lessthan the longitudinal focus (LGF) of critical point P4, critical pointP4 is displaced along the P4 moving line (effectively narrowing the wideideal tripole configuration). In this case, the critical points P4, P5are concurrently displaced along the respective P4, P5 moving lines tothe same longitudinal focus (LGF) value and the same upper anodepercentage (UAP) value. In effect, the critical points P4, P5 willrepresent the identical ideal tripole configuration.

As shown in FIG. 28b , critical points P3, P5, P6 are displaced inaccordance with three different rostral maximum longitudinal focuses(LGFs) (represented by vertical solid lines) that are between thelongitudinal focuses (LGFs) of critical points P4, P6. As shown in FIG.28c , critical points P2, P3, P4, P5 are displaced in accordance withtwo different rostral maximum longitudinal focuses (LGFs) (representedby vertical solid lines) that are less than the longitudinal focus (LGF)of critical point P4. Shifting of the ideal cathode may be appliedbetween critical points P3, P6. A modified weaving trajectory linesequentially connects the modified critical points P1-P7 shown in FIGS.28b and 28 c.

Notably, there may be times when the anodes of the ideal bipole/tripoleconfigurations must be eliminated from the sequence, because the idealcathode is too close to the maximum extent of the electrode array 26.For example, as shown in FIG. 29, as a result of the ideal cathode beingtoo close to the maximum rostral extent of the electrode array 26, theupper anode of the ideal bipole/tripole configurations cannot be used.In this case, the sequence of ideal bipole/tripole configurations shownin FIG. 24 will be limited to lower ideal bipole configurations (i.e.,the narrow lower ideal bipole configuration (B_(2l)), (adjusted) widelower ideal bipole configuration (B_(2.5l)), and wide lower ideal bipoleconfiguration (B_(3l)).

As best shown in FIG. 30, the sequence of ideal lower bipoleconfigurations is defined by a trajectory line sequentially connectingthe critical points (representing by circles). As can be seen, thesequence beginning with the narrow lower ideal bipole configuration(B_(2l)) and ending with the (adjusted) wide lower ideal bipoleconfiguration (B_(2.5l)) incrementally increases the longitudinal focus(LGF) while displacing the ideal cathode. The sequence beginning withthe wide lower ideal bipole configuration (B_(2.5l)) and ending with thewide lower ideal bipole configuration (B_(3l)) further incrementallyincreases the longitudinal focus (LGF) while further displacing theideal cathode. The sequence beginning with the wide lower ideal bipoleconfiguration (B_(3l)) and ending with the narrow lower ideal bipoleconfiguration (B_(2l)) incrementally decreases the longitudinal focus(LGF) while maintaining the ideal cathode.

Although the techniques for preventing ideal multipole configurationsfrom exceeding the maximum extent of the electrode array 26 have beendescribed above with respect to longitudinal bipole/tripoleconfigurations, it should be appreciated that techniques for preventingthe ideal multipole configurations from exceeding the maximum extent ofthe electrode array 26 can be applied to the transverse multipoleconfigurations illustrated in FIG. 22 b.

As previously discussed, it is preferable that the spacings between thepoles of the ideal multiple configurations (i.e., the focuses) match theeffective separation between the electrodes 26. In performing thisfunction, the CP 18 is capable of estimating an effective electrodeseparation between the physical electrodes 26 and estimating aneffective electrode separation at an arbitrary point in space bounded bythe physical electrodes 26.

Referring first to FIGS. 31a and 31b , an ideal longitudinal tripoleconfiguration is shown relative to three percutaneous neurostimulationleads 12(1)-12(3) that are longitudinally staggered relative to eachother. As shown, neurostimulation leads 12(1) and 12(2) carry eightelectrodes 26 each, and the neurostimulation lead 12(3) carries fourelectrodes 26.

As shown in FIG. 31a , when the pole axis 290 along which the poles ofthe ideal tripole configuration are aligned is parallel to thelongitudinal axis of the center lead 12(2), with the ideal cathode 252being located on one of the electrodes 26 (center electrode), assumingthat a longitudinal focus equal to a two electrode separation isdesired, the effective electrode separation is estimated to simply bethe same as the electrode separation for the center lead 12(2), so thatthe ideal anodes 254 are located over the second electrodes from thecenter electrode over which the ideal cathode 252 is located.

However, as shown in FIG. 31b , when the pole axis 290 has been rotatedrelative to the longitudinal axis of the center lead 12(2), with theideal cathode 252 being located on one of the electrodes 26, theeffective electrode separation is estimated based on the availableelectrodes 26 along the pole axis 290. To obtain a longitudinal focuswith a two electrode separation, an initial effective electrodeseparation from the center electrode is estimated along the pole axis290 to obtain an estimation of the first electrode location (representedby the diamond), and then a second effective electrode separation fromthe estimated first electrode location is then estimated to obtain anestimation of the second electrode location.

With reference to FIG. 32a , two staggered neurostimulation leads 12(1),12(2) are shown with a total of six electrodes E1-E6. It is assumed thatthe CP 18 will define an ideal multipole configuration relative to theelectrodes E1-E6 in alignment with a pole axis 290. In the illustratedembodiment, the neurostimulation leads 12(1), 12(2) are parallel to eachother and/or the pole axis 290 is parallel to the neurostimulation leads12(1), 12(2). However, it should be noted that the neurostimulationleads 12(1), 12(2) may be non-parallel to each other and/or the poleaxis 290 may be non-parallel to either of the neurostimulation leads12(1), 12(2).

In attempting to match the focus of the ideal multiple configurationwith the effective electrode separation along the pole axis 290, the CP18 designates each of the electrodes E1-E6 as a reference electrode,estimates an effective electrode separation at each of the E1-E6,estimates an effective electrode separation at a point in space (x, y)along the pole axis 290 (presumably, where one pole of the idealmultiple configuration is located) based on the estimated effectiveelectrode separation at each of the reference electrodes E1-E6, anddefines the spacing between the poles (i.e., the focus) of the idealmultiple configuration based on the estimated effective electrodeseparation at the point in space (x, y) along the pole axis 290.

In the illustrated embodiment, the CP 18 estimates the effectiveelectrode separation at each of the reference electrodes E1-E6 bycomputing a weighted average of actual separations between eachrespective reference electrode and the indexed ones of the electrodes.For each reference electrode, the CP 18 will select only the electrodesthat are located in the direction in which the effective electrodeseparation is estimated. In the illustrated embodiment, the CP 18selects, as the indexed electrodes, only the electrodes located on oneside of a line 292 intersecting the respective reference electrode andperpendicular to the pole axis 290; that is, all of the electrodes abovethe line 292 if the effective electrode separation in the rostraldirection is estimated, and all of the electrodes below the line 292 ifthe effective electrode separation in the caudal direction is estimated.For example, if the current reference electrode is electrode E5, and theeffective electrode separation is to be estimated in the rostraldirection, the CP will determine the respective spacings betweenreference electrode E5 and indexed electrodes E1, E2, and E4, which areall above the line 292. If the current reference electrode is electrodeE5, and the effective electrode separation is to be estimated in thecaudal direction, the CP will determine the respective spacings betweenreference electrode E5 and indexed electrodes E3 and E6, which are bothbelow the line 292.

For each reference electrode, weighting values are given to the indexedelectrodes in accordance with the separation between the referenceelectrode and the indexed electrode, such that the indexed electrodesthat are relatively close to the reference electrode are givenrelatively high weighting values, and the indexed electrodes that arerelatively far from the reference electrode are given relatively lowweighting values. Thus, it can be appreciated when the neurostimulationleads 12 are widely spaced apart, as shown in FIG. 32b , the indexedelectrodes on the right neurostimulation lead 12(2) may be too far froma reference electrode (in this case, electrode E2 represented by thecircle) on the left neurostimulation lead 12(1) to be considered, andthus, the effective electrode separation will approach the nominalelectrode separation on the neurostimulation leads 12 (e.g., 8 mm). Whenthe neurostimulation leads 12 are narrowly spaced apart, as shown inFIG. 32c , the indexed electrodes on the right neurostimulation lead12(2) may be close enough to the reference electrode (in this case,electrode E2 represented by the circle) on the left neurostimulation12(1) to dominate, and thus, the effective electrode separation willapproach the separation between the reference electrode E2 and electrodeE4 (e.g., 4 mm if electrode E4 is equidistance between electrodes E1 andE2).

Referring to FIG. 33, one method of estimating the effective electrodeseparation of electrodes E1-E6 at a point in space (x, y) in the rostraldirection will now be described.

First, one of the electrodes E1-E6 is currently designated as areference electrode j (step 300). Next, it is determined whether thereare any electrodes above the currently designated reference electrode j,and in particular, above a line that is perpendicular to the pole axisand intersects the currently designated reference electrode j (step301). If there are any electrodes above the currently designatedreference electrode j, all of these electrodes are identified as indexedelectrodes j to be compared to the currently designated referenceelectrode j (step 302). Next, one of the indexed electrodes i isselected (step 303), and the actual separation between the currentlydesignated reference electrode j and the currently selected indexedelectrode i is computed (step 304).

In the illustrated embodiment, the actual separation is represented by afirst directional component d_(x) perpendicular to the pole axis 290 anda second directional component d_(y) perpendicular to the pole axis 290.The first directional component d_(x) can be computed in accordance withthe equation: d_(x)=|x−E_(x)(i)|, where x is the coordinate of thecurrently designated reference electrode j along an axis perpendicularto the pole axis 290, and Ex is the coordinate of the currently selectedindexed electrode i along an axis perpendicular to the pole axis 290.The second directional component d_(y) can be computed in accordancewith the equation: d_(y)=|y−E_(y)(i)|, where y is the coordinate of thecurrently designated reference electrode j along an axis parallel to thepole axis 290, and E_(y) is the coordinate of the currently selectedindexed electrode i along an axis parallel to the pole axis 290.

Then, weighting values W_(x) and W_(y) for the indexed electrode i arerespectively computed from the first directional separation componentd_(x) and second directional separation component d_(y) (step 305). Theweighting value Wx for the indexed electrode i can be computed inaccordance with the equation: W_(x)(i)=e^((−d) ^(x) ^(·λ) ^(x) ⁾, whereλ_(x) is a constant. The weighting value Wy for the indexed electrode ican be computed in accordance with the equation: W_(y)(i)=e^((−d) ^(y)^(·λ) ^(y) ⁾, where λ_(y) is a constant. In the illustrated embodiment,λ_(x) is greater than λ_(y). For example, λ_(x) may be equal to 5, andλ_(y) may be equal to 1. In this manner, the component of the actualspacing along the pole axis 202 is weighted greater than the componentof the actual spacing perpendicular to the pole axis 202.

Notably, because there is a limit to how close ideal poles can be beforeelectrical performance degrades, it is important that electrodes thatare too close to the reference electrode be eliminated from theeffective electrode separation estimation. To this end, it is determinedwhether the separation, and in particular the second directionalcomponent d_(y) of the actual separation, between the selected indexedelectrode i and the currently designated reference electrode j is lessthan a minimum threshold value (e.g., 3.8 mm) (step 306). If the seconddirectional component d_(y) is less than the minimum threshold value,the currently selected indexed electrode i is eliminated from theeffective electrode separation estimation by designating a discreteweighting value w_(c)(i)=0 (step 307). If the second directionalcomponent d_(y) is not less than the minimum threshold value, thecurrently selected indexed electrode i is considered in the effectiveelectrode separation estimation by designating a discrete weightingvalue w_(c)(i)=1 (step 308).

Next, it is determined whether all of the indexed electrodes i have beenselected for comparison with the currently designated referenceelectrode j (step 309). If not, steps 303-308 are repeated for the nextindexed electrode i. If so, it is determined whether any of the selectedindexed electrodes i has been selected to be considered in the electrodeseparation estimation (i.e., whether any indexed electrode i has anon-zero discrete weighting w_(c)(i)) (step 310). If at least oneselected indexed electrode i has a non-zero discrete weighting w_(c)(i),the effective electrode separation at the currently designated referenceelectrode j is estimated by computing a weighted average of actualseparations between the currently designated reference electrode j andindexed electrodes i in accordance with the equation (step 311):

$S_{e} = {\frac{\sum\limits_{i}^{N}{{W_{x}(i)} \cdot {W_{y}(i)} \cdot {W_{c}(i)} \cdot {d_{y}(i)}}}{\sum\limits_{i}^{N}{{W_{x}(i)} \cdot {W_{y}(i)}}}.}$

If there are no electrodes above the currently designated referenceelectrode j, as determined in step 301, or if no indexed electrode i hasa non-zero discrete weighting w_(c)(i), as determined in step 310, theeffective electrode separation at the currently designated referenceelectrode j is set to a maximum value (e.g., 12 mm) (step 312).

Next, it is determined whether all the electrodes have been designatedas reference electrodes j (step 313). If not, steps 300-312 are repeatedfor the next reference electrode j. If so, an effective electrodeseparation at a point in space (x, y) along the pole axis 290 isdetermined by computing a weighted average of the estimated effectiveelectrode separations at all of the reference electrodes j in accordancewith the equation:

${S_{s} = \frac{\sum\limits_{i}^{N}{{W_{x}(j)} \cdot {W_{y}(j)} \cdot {S_{e}(j)}}}{\sum\limits_{i}^{N}{{W_{x}(j)} \cdot {W_{y}(j)}}}},$where S_(s) is the effective electrode separation at the point in space,j is the index for one of the reference electrodes, N is the totalnumber of the reference electrodes, W_(x) is a weighting value as afunction of the first directional component of the distance between thepoint in space and the reference electrode j, W_(y) is a weighting valueas a function of the second directional component of the distancebetween the point in space and the reference electrode j, and Se is theestimated effective electrode separation at the reference electrode j.

In the illustrated embodiment, the weighting values W_(x) and W_(y) arecomputed in accordance with the equations: W_(x)(j)=e^((−|x-E) ^(x)^((j)|·λ) ^(x) ⁾ and W_(y)(j)=e^((−|y-E) ^(y) ^((j)|·λ) ^(y) ⁾, whereλ_(x), and λ_(y) are constants, x is the coordinate of the point inspace along an axis perpendicular to the pole axis 290, y is thecoordinate of the point in space along the pole axis 290, E_(x) is thecoordinate of the position of the reference electrode j along an axisperpendicular to the pole axis 290, and E_(y) is the coordinate of theposition of the reference electrode j along the pole axis 290.

To prevent the effective electrode separation at a point in space fromexceeding a maximum value, maximum electrode separations at a pluralityof imaginary reference electrodes (E1′-E6′) surrounding the actualreference electrodes j can be assumed, as illustrated in FIG. 32a . Inthe illustrated embodiments the total number of imaginary referenceelectrodes E1′-E6′ are twice the total number of actual referenceelectrodes. In particular, a pair of imaginary reference electrodes isassociated with each actual reference electrode. The pair of imaginaryreference electrodes are aligned with the y-coordinate of the respectiveactual reference electrode, and are respectively located on two lines294 that are parallel to the pole axis 290 and located outside of theactual reference electrodes (e.g., a left line that is 4 mm to the leftof the left-most reference electrode, and a right line that is 4 mm thatis 4 mm to the right of the right-most reference electrode). The maximumeffective electrode separation at each respective imaginary referenceelectrode can be selected to be a maximum value (e.g., 12 mm). Theimaginary reference electrode can be taken into account when estimatingthe effective electrode separation in space by including the imaginaryreference electrodes in addition to the actual reference electrodes inthe estimation.

Assuming that the point in space (x, y) is coincident with a pole of theideal multipole configuration (e.g., an ideal cathode in an upper anodebipole configuration or tripole configuration) to be defined, thelocation of the other pole (e.g., an ideal anode) can be set to be adistance in the rostral direction equal to the estimated effectiveelectrode separation at the point in space (x, y). In the case where itis desirable to define the location of an pole in the caudal direction,the effective electrode separation at the point in space (x, y) isperformed in the same manner discussed with respect to FIG. 32, with theexception that the electrodes below each currently designated referenceelectrode j are selected as the indexed electrodes i, and in particular,below a line that is perpendicular to the pole axis and intersects therespective designated reference electrode j.

Although the foregoing techniques have been described as beingimplemented in the CP 18, it should be noted that this technique may bealternatively or additionally implemented in the RC 16, and theprocessing functions of the technique can even be performed in the IPG14.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

What is claimed is:
 1. A system for an electrical neurostimulatorcoupled to an array of electrodes having a maximum extent, comprising: auser-controlled input device configured for generating directionalcontrol signals; memory storing a plurality of target configurations,each target configuration having at least one pole that can be emulatedwith a fractionalized current or voltage applied to the array ofelectrodes; and control circuitry configured for defining the pluralityof target configurations relative to the electrode array in response tothe directional control signals, the control circuitry configured fordetermining a spatial relationship between at least one of the definedplurality of target configurations and the maximum extent of theelectrode array, the control circuitry configured for modifying thedefined plurality of the target configurations based on the determinedspatial relationship, such that the modified plurality of the targetconfigurations is spatially within the maximum extent of the electrodearray, the control circuitry configured for generating a plurality ofstimulation parameter sets respectively corresponding to the modifiedplurality of target configurations, each stimulation parameter setdefining relative amplitude values for the electrode array that emulatethe respective modified target configuration, and the control circuitryconfigured for instructing the electrical neurostimulator to conveyelectrical energy to the electrode array in accordance with theplurality of stimulation parameter sets.
 2. The system of claim 1,wherein the electrode array is a linear electrode array, and the maximumextent is coincident with an electrode at the end of the linearelectrode array.
 3. The system of claim 1, wherein the targetconfigurations comprise at least one bipole configuration and at leastone tripole configuration.
 4. The system of claim 1, wherein the atleast one defined target configuration comprises more than one definedtarget configuration.
 5. The system of claim 1, wherein the controlcircuitry is configured for modifying the defined plurality of targetconfigurations by eliminating one or more of the at least one definedtarget configuration.
 6. The system of claim 1, wherein the controlcircuitry is configured for modifying the defined plurality of targetconfigurations by modifying when a pole of the same polarity isinitially displaced during the at least one defined targetconfiguration.
 7. The system of claim 1, wherein the control circuitryis configured for modifying the defined plurality of targetconfigurations by displacing a pole for one or more of the at least onedefined target configuration.
 8. The system of claim 1, wherein thecontrol circuitry is configured for modifying the defined plurality oftarget configurations by displacing poles of different polaritiesrelative to each other for one or more of the at least one definedtarget configuration.
 9. The system of claim 8, wherein the memory, foreach of the at least one defined target configuration, stores a variablevalue defining a spatial relationship between the poles of the differentpolarities, and the control circuitry is configured for displacing thepoles of different polarities relative to each other for the at leastone target configuration by modifying the respective at least onevariable value.
 10. The system of claim 9, wherein the control circuitryis configured for modifying the respective one or more variable valuesby decreasing the one or more variable values.
 11. The system of claim9, wherein the variable value for each of the at least one definedtarget configuration defines an absolute distance between the poles ofthe different polarities.
 12. The system of claim 9, wherein the definedplurality of target configurations includes a defined plurality of widebipole/tripole configurations and a defined plurality of narrowbipole/tripole configurations, the at least one defined targetconfiguration includes the defined plurality of wide bipole/tripoleconfigurations, and the control circuitry is configured for displacingthe poles of different polarities relative to each other for the atleast one target configuration by decreasing the respective at least onevariable value.
 13. The system of claim 12, wherein the definedplurality of narrow bipole/tripole configurations initially comprises anarrow upper bipole configuration and a narrow lower bipoleconfiguration, and the defined plurality of wide bipole/tripoleconfigurations initially comprises two identical wide upper bipoleconfigurations, a first wide tripole configuration, and two identicalwide lower bipole configurations.
 14. The system of claim 13, whereinthe control circuitry is configured for decreasing the variable valuesassociated with a first one of the two identical wide upper bipoleconfigurations and a first one of the two identical wide lower bipoleconfigurations to a first identical value.
 15. The system of claim 14,wherein the control circuitry is configured for changing one of a secondone of the two identical wide upper bipole configurations and a secondone of the two identical wide lower bipole configurations to a secondwide tripole configuration, and modifying a relative intensity betweenthe poles of different polarities of the second wide tripoleconfiguration.
 16. The system of claim 15, wherein the control circuitryis configured for decreasing the variable value associated with thesecond wide tripole configuration.
 17. The system of claim 16, whereinthe control circuitry is configured for decreasing the variable valueassociated with the second wide tripole configuration to the firstidentical value.
 18. The system of claim 1, wherein the user-controlinput device includes a control element, a continual actuation of whichgenerates the directional control signals.
 19. The system of claim 1wherein the control circuitry is further configured to deliver anelectrical current to at least one electrode in the electrode array, thedelivered current being independent of a current delivered to otherelectrodes in the electrode array.
 20. A system for an electricalneurostimulator coupled to an array of electrodes having a maximumextent, comprising: a user-controlled input device configured forgenerating directional control signals; memory storing a plurality oftarget configurations, each target configuration having at least onepole that can be emulated with a fractionalized current or voltageapplied to the array of electrodes; and control circuitry configured fordefining the plurality of target configurations relative to theelectrode array in response to the directional control signals, thecontrol circuitry configured for determining a spatial relationshipbetween at least one of the defined plurality of target configurationsand the maximum extent of the electrode array, the control circuitryconfigured for modifying the defined plurality of the targetconfigurations based on the determined spatial relationship, such thatthe modified plurality of the target configurations is spatially withinthe maximum extent of the electrode array, the control circuitryconfigured for generating a plurality of stimulation parameter setsrespectively corresponding to the modified plurality of targetconfigurations, each stimulation parameter set defining relativeamplitude values for the electrode array that emulate the respectivemodified target configuration, and the control circuitry configured forinstructing the electrical neurostimulator to convey electrical energyto the electrode array in accordance with the plurality of stimulationparameter sets, wherein the electrode array is a linear electrode array,and the maximum extent is coincident with an electrode at the end of thelinear electrode array, and the control circuitry is configured formodifying the defined plurality of target configurations by eliminatingone or more of the at least one defined target configuration.